event handler > automation > enter the time when a cell is changed >macros that respond to events are very picky about where they are stored. For example, this Worksheet_Change macro must be in the Code module for that worksheet. Put it somewhere else, and it won’t work.
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Column = 1 Then
Target.Offset(0, 1) = Now
End If
End Sub