Option Explicit
Private Sub Worksheet_Change(ByVal c As Range)
On Error Resume Next
If c.Row = 1 Then Rows("1:1").SpecialCells(xlCellTypeConstants, 23).Offset(1, 0).FormulaR1C1 = "=TODAY()"
' ou, pour une date figée
' If c.Row = 1 Then Rows("1:1").SpecialCells(xlCellTypeConstants, 23).Offset(1, 0) = Date
End Sub