Sub remplir()
Columns("C:C").NumberFormat = "dd/mm/yyyy hh:mm:ss"
tablo = Range("B1:C" & Range("B" & Rows.Count).End(xlUp).Row)
tablo(1, 2) = tablo(1, 1)
For n = LBound(tablo, 1) + 1 To UBound(tablo, 1)
tablo(n, 2) = tablo(1, 1) + tablo(n, 1)
Next
Range("B1").Resize(UBound(tablo, 1), UBound(tablo, 2)) = tablo
End Sub