Non, il ne faut pas coller des baffes aux clients qui ... paient.
A la place, si l'on suppose que les dates seront mises dans la colonne B, à partir de B2, voici comment les formatter :
|   LineCount = rst.RecordCount
For iLine = 1 To LineCount
 xlWs.Cells(iLine + 1, 2).NumberFormat = "dd/mm/yyyy"
 Next
 | 
En prime, il est possible d'ajuster la largeur et la hauteur des colonnes : 
|   xlApp.Selection.CurrentRegion.Columns.AutoFit
xlApp.Selection.CurrentRegion.Rows.AutoFit
 
 | 
 Et pourquoi ne pas aussi insérer le titre des colonnes ? Pendant que j'y suis, voici mon exemple en entier :
| 'Extract data to excel file
Private Sub B_export2excel_Click()
 
 Dim SQL_ligne As String, s As String
 'Dim bds As Database, rst As Recordset
 
 ' Retrieve data from table
 SQL_ligne = "SELECT id, date1, text1" & _
 " FROM T_test;"
 Set bds = CurrentDb
 Set rst = bds.OpenRecordset(SQL_ligne)
 
 ' Create an instance of Excel and add a workbook
 Set xlApp = CreateObject("Excel.Application" )
 Set xlWb = xlApp.Workbooks.Add
 Set xlWs = xlWb.Worksheets(1)
 
 ' Display Excel and give user control of Excel's lifetime
 xlApp.Visible = True
 xlApp.UserControl = True
 
 ' Copy field names to the first row of the worksheet
 fldCount = rst.Fields.Count
 For iCol = 1 To fldCount
 xlWs.Cells(1, iCol).Value = rst.Fields(iCol - 1).Name
 Next
 
 ' Copy entire recordset to excel starting from A2
 xlWs.Cells(2, 1).CopyFromRecordset rst
 
 ' Change the format
 LineCount = rst.RecordCount
 For iLine = 1 To LineCount
 '     xlWs.Cells(iLine + 1, 2).NumberFormat = "yyyymmdd"
 xlWs.Cells(iLine + 1, 2).NumberFormat = "dd/mm/yyyy"
 Next
 
 ' Auto-fit the column widths and row heights
 xlApp.Selection.CurrentRegion.Columns.AutoFit
 xlApp.Selection.CurrentRegion.Rows.AutoFit
 
 ' Save an Excel file from MS Access using VBA
 xlApp.Application.ActiveWorkbook.SaveAs FileName:="c:\DEV\XL_test.xls"
 
 'Close the recordset
 rst.Close
 
 ' Quit Excel
 xlApp.Quit
 
 End Sub
 
 | 
 