Private Sub Worksheet_Change(ByVal Target As Range)
Dim rng As Range, cell As Range
Set rng = Intersect(Target, Range("A:A")) 'amend Range("A:A") to be whichever column holds your comments
If Not rng Is Nothing Then
Application.EnableEvents = False
For Each cell In rng
If Not IsEmpty(cell.Value) Then
cell.Offset(, 1).Value = Date
Else
cell.Offset(, 1).ClearContents
End If
Next cell
Application.EnableEvents = True
End If
End Sub