I guess, you need below.. paste this code in worksheet module..

Option Explicit


Private Sub Worksheet_Change(ByVal Target As Range)
    Dim KeyCells As Range


    ' The variable KeyCells contains the cells that will
    ' cause an alert when they are changed.
    Set KeyCells = Range("M19")
    
    If Not Application.Intersect(KeyCells, Range(Target.Address)) _
           Is Nothing Then


        ' Display a message when one of the designated cells has been
        ' changed.
        ' Place your code here.
        Range("L16").Value = Time
       
    End If
End Sub


Cheers!!