procedure TForm1.MicrosoftExcelTimeFormatting(Sender: TObject);
var
   ExcelFileName: String;
   ExcelApplication, ExcelWorkbook, ExcelWorksheet: Variant;
begin
     //be sure ComObj and Variants units are included in the "uses" clause

     ExcelFileName := 'C:\PhysiologyWeb\delphi_code_examples\excel_file_time_formatting.xlsx'; //replace file name with the name of your file

     ExcelApplication := Null;
     ExcelWorkbook := Null;
     ExcelWorksheet := Null;

     try
        //create Excel OLE
        ExcelApplication := CreateOleObject('Excel.Application');
     except
           ExcelApplication := Null;
           //add error/exception handling code as desired
     end;

     If VarIsNull(ExcelApplication) = False then
        begin
             try
                ExcelApplication.Visible := True; //set to False if you do not want to see the activity in the background
                ExcelApplication.DisplayAlerts := False; //ensures message dialogs do not interrupt the flow of your automation process. May be helpful to set to True during testing and debugging.

                //Open Excel Workbook
                try
                   ExcelWorkbook := ExcelApplication.WorkBooks.Add(-4167);
                   //reference
                   //https://docs.microsoft.com/en-us/office/vba/api/excel.workbooks.add
                   //https://docs.microsoft.com/en-us/office/vba/api/excel.xlsheettype
                except
                      ExcelWorkbook := Null;
                      //add error/exception handling code as desired
                end;

                If VarIsNull(ExcelWorkbook) = False then
                   begin
                        //connect to Excel Worksheet using either the ExcelApplication or ExcelWorkbook handle
                        try
                           ExcelWorksheet := ExcelWorkbook.WorkSheets[1]; //[1] specifies the first worksheet
                           //reference
                           //https://docs.microsoft.com/en-us/office/vba/api/Excel.Worksheets.Item
                        except
                              ExcelWorksheet := Null;
                              //add error/exception handling code as desired
                        end;

                        If VarIsNull(ExcelWorksheet) = False then
                           begin
                                ExcelWorksheet.Select;

                                //add text to A1 cell [row,column]
                                ExcelWorksheet.Cells[1,1] := 'Microsoft Excel - Cell Number Formatting - Time Formatting';
                                //change the font size in A1 cell
                                ExcelWorksheet.Cells[1,1].Font.Size := 20;
                                //make A1 cell font bold
                                ExcelWorksheet.Cells[1,1].Font.Bold := True;
                                //change font color to blue
                                ExcelWorksheet.Cells[1,1].Font.Color := clBlue;
                                //change background color of A1 cell
                                ExcelWorksheet.Cells[1,1].Interior.Color := clYellow;

                                //add text to A3 cell [row,column]
                                ExcelWorksheet.Cells[3,1] := 'Hold your mouse over cells with numbers to see comments.';

                                //add text to A5 cell [row,column]
                                ExcelWorksheet.Cells[5,1] := 'Time Format';
                                ExcelWorksheet.Cells[5,1].Font.Bold := True;
                                ExcelWorksheet.Cells[5,1].Interior.Color := clAqua;

                                //add text to B5 cell [row,column]
                                ExcelWorksheet.Cells[5,2] := 'Format Code';
                                ExcelWorksheet.Cells[5,2].Font.Bold := True;
                                ExcelWorksheet.Cells[5,2].Interior.Color := clAqua;

                                //add text to C5 cell [row,column]
                                ExcelWorksheet.Cells[5,3] := 'Format Description';
                                ExcelWorksheet.Cells[5,3].Font.Bold := True;
                                ExcelWorksheet.Cells[5,3].Interior.Color := clAqua;

                                //add date and time, code, and description to row 6 [row,column]
                                ExcelWorksheet.Cells[6,1] := '=now()'; //adds today's date to A6 cell
                                ExcelWorksheet.Cells[6,1].AddComment('Default date and time format');
                                ExcelWorksheet.Cells[6,3] := 'Default date and time format';

                                //add date and time, code, and description to row 7 [row,column]
                                ExcelWorksheet.Cells[7,1] := '=now()';
                                ExcelWorksheet.Cells[7,1].NumberFormat := 'm/d/yyyy hh:mm:ss AM/PM';
                                ExcelWorksheet.Cells[7,1].AddComment('Date and time format: month/day/year hour:minute:second. 1 or 2 digits for month and day. 2 digits for hour, minute, and second. AM/PM format.');
                                ExcelWorksheet.Cells[7,2] := 'm/d/yyyy hh:mm:ss AM/PM';
                                ExcelWorksheet.Cells[7,3] := 'Date and time format: month/day/year hour:minute:second. 1 or 2 digits for month and day. 2 digits for hour, minute, and second. AM/PM format.';

                                //add date and time, code, and description to row 8 [row,column]
                                ExcelWorksheet.Cells[8,1] := '=now()';
                                ExcelWorksheet.Cells[8,1].NumberFormat := 'm/d/yyyy h:m:s AM/PM';
                                ExcelWorksheet.Cells[8,1].AddComment('Date and time format: month/day/year hour:minute:second 1 or 2 digits for month and day. 1 or 2 digits for hour, minute, and second. AM/PM format.');
                                ExcelWorksheet.Cells[8,2] := 'm/d/yyyy h:m:s AM/PM';
                                ExcelWorksheet.Cells[8,3] := 'Date and time format: month/day/year hour:minute:second 1 or 2 digits for month and day. 1 or 2 digits for hour, minute, and second. AM/PM format.';

                                //add date and time, code, and description to row 9 [row,column]
                                ExcelWorksheet.Cells[9,1] := '=now()';
                                ExcelWorksheet.Cells[9,1].NumberFormat := 'mm/dd/yyyy hh:mm:ss';
                                ExcelWorksheet.Cells[9,1].AddComment('Date and time format: month/day/year hour:minute:second. 2 digits for month and day. 2 digits for hour, minute, and second. 24-hour time format.');
                                ExcelWorksheet.Cells[9,2] := 'mm/dd/yyyy hh:mm:ss';
                                ExcelWorksheet.Cells[9,3] := 'Date and time format: month/day/year hour:minute:second. 2 digits for month and day. 2 digits for hour, minute, and second. 24-hour time format.';

                                //add date and time, code, and description to row 10 [row,column]
                                ExcelWorksheet.Cells[10,1] := '=now()';
                                ExcelWorksheet.Cells[10,1].NumberFormat := 'hh:mm:ss AM/PM';
                                ExcelWorksheet.Cells[10,1].AddComment('Time format: hour:minute:second. 2 digits for hour, minute, and second. AM/PM format.');
                                ExcelWorksheet.Cells[10,2] := 'hh:mm:ss AM/PM';
                                ExcelWorksheet.Cells[10,3] := 'Time format: hour:minute:second. 2 digits for hour, minute, and second. AM/PM format.';

                                //add date and time, code, and description to row 11 [row,column]
                                ExcelWorksheet.Cells[11,1] := '=now()';
                                ExcelWorksheet.Cells[11,1].NumberFormat := '[$]hh:mm:ss a/p"m";@';
                                ExcelWorksheet.Cells[11,1].AddComment('Time format: hour:minute:second. 2 digits for hour, minute, and second. am/pm format (lower case).');
                                ExcelWorksheet.Cells[11,2] := '[$]hh:mm:ss a/p"m";@';
                                ExcelWorksheet.Cells[11,3] := 'Time format: hour:minute:second. 2 digits for hour, minute, and second. am/pm format (lower case)';

                                //add date and time, code, and description to row 12 [row,column]
                                ExcelWorksheet.Cells[12,1] := '=now()';
                                ExcelWorksheet.Cells[12,1].NumberFormat := 'hh:mm:ss';
                                ExcelWorksheet.Cells[12,1].AddComment('Time format: hour:minute:second. 2 digits for hour, minute, and second. 24-hour time format.');
                                ExcelWorksheet.Cells[12,2] := 'hh:mm:ss';
                                ExcelWorksheet.Cells[12,3] := 'Time format: hour:minute:second. 2 digits for hour, minute, and second. 24-hour time format.';

                                //add date and time, code, and description to row 13 [row,column]
                                ExcelWorksheet.Cells[13,1] := '=now()';
                                ExcelWorksheet.Cells[13,1].NumberFormat := 'hh:mm AM/PM';
                                ExcelWorksheet.Cells[13,1].AddComment('Time format: hour:minute. 2 digits for hour and minute. AM/PM format.');
                                ExcelWorksheet.Cells[13,2] := 'hh:mm AM/PM';
                                ExcelWorksheet.Cells[13,3] := 'Time format: hour:minute. 2 digits for hour and minute. AM/PM format.';

                                //add date and time, code, and description to row 14 [row,column]
                                ExcelWorksheet.Cells[14,1] := '=now()';
                                ExcelWorksheet.Cells[14,1].NumberFormat := 'hh:mm';
                                ExcelWorksheet.Cells[14,1].AddComment('Time format: hour:minute. 2 digits for hour and minute. 24-hour time format.');
                                ExcelWorksheet.Cells[14,2] := 'hh:mm';
                                ExcelWorksheet.Cells[14,3] := 'Time format: hour:minute. 2 digits for hour and minute. 24-hour time format.';

                                //add date and time, code, and description to row 15 [row,column]
                                ExcelWorksheet.Cells[15,1] := '=now()';
                                ExcelWorksheet.Cells[15,1].NumberFormat := 'General';
                                ExcelWorksheet.Cells[15,1].AddComment('Time format: General. Date and time are shown as a number and fraction.');
                                ExcelWorksheet.Cells[15,2] := 'General';
                                ExcelWorksheet.Cells[15,3] := 'Time format: General. Date and time are shown as a number and fraction.';

                                //add date and time, code, and description to row 16 [row,column]
                                ExcelWorksheet.Cells[16,1] := '=now()';
                                ExcelWorksheet.Cells[16,1].NumberFormat := '[$]hh:mm;@';
                                ExcelWorksheet.Cells[16,1].AddComment('Time format: hour:minute. 2 digits for hour and minute. 24-hour time format.');
                                ExcelWorksheet.Cells[16,2] := '[$]hh:mm;@';
                                ExcelWorksheet.Cells[16,3] := 'Time format: hour:minute. 2 digits for hour and minute. 24-hour time format.';

                                ExcelWorksheet.Cells[17,1] := '=now()';
                                ExcelWorksheet.Cells[17,1].NumberFormat := '[$-F400]h:mm:ss AM/PM';
                                ExcelWorksheet.Cells[17,1].AddComment('Time format set to default system format.');
                                ExcelWorksheet.Cells[17,2] := '[$-F400]h:mm:ss AM/PM';
                                ExcelWorksheet.Cells[17,3] := 'Time format set to default system format.';

                                //references
                                //https://learn.microsoft.com/en-us/office/vba/api/excel.cellformat.numberformat
                                //https://learn.microsoft.com/en-us/dotnet/api/documentformat.openxml.spreadsheet.numberingformat
                                //https://support.microsoft.com/en-us/office/number-format-codes-5026bbd6-04bc-48cd-bf33-80f18b4eae68?ui=en-us&rs=en-us&ad=us
                                //https://learn.microsoft.com/en-us/office/vba/api/Access.format.propertydate.time
                                //https://support.microsoft.com/en-us/office/cell-function-51bd39a5-f338-4dbe-a33f-955d67c2b2cf

                                //autofit the width of Column A
                                ExcelWorksheet.Columns[1].EntireColumn.AutoFit; //autofits Column A
                                ExcelWorksheet.Columns[2].EntireColumn.AutoFit; //autofits Column A
                                ExcelWorksheet.Columns[3].EntireColumn.AutoFit; //autofits Column A
                                //reference
                                //https://docs.microsoft.com/en-us/office/vba/api/excel.range.autofit

                                //select A1 cell
                                ExcelWorksheet.Cells[1,1].Select; //selects Cell A1

                                ExcelWorkbook.SaveAs(ExcelFileName);
                                //Note: If a file with the new name already exists, it overwrites it. Write additional code to address as desired.
                                //reference
                                //https://docs.microsoft.com/en-us/office/vba/api/excel.workbook.saveas
                           end;
                   end;
             finally
                    ExcelApplication.Workbooks.Close;
                    ExcelApplication.DisplayAlerts := True;
                    ExcelApplication.Quit;

                    ExcelWorksheet := Unassigned;
                    ExcelWorkbook := Unassigned;
                    ExcelApplication := Unassigned;
             end;
        end;
end;