Macro To Set Current Time In A Cell Without Changing Similar Values In Other Cells

I have a Macro 'Timenow' to give current time in a Cell of MS Excel, but then it changes all Cell values of sheet where the macro was used.

Sub Timenow()
'
' Timenow Macro
' Keyboard Shortcut: Ctrl+b
ActiveCell.FormulaR1C1 = "=NOW()"
Selection.NumberFormat = "h:mm"
Range("F5").Select
End Sub

Even assigning value to variable does not work:

Sub Timenow()
' Timenow Macro
' Keyboard Shortcut: Ctrl+b
Dim TN As String
TN = Format("=now()", "h:mm")
ActiveCell.Value = TN
End Sub

how to restrict the macro to change the value of current/active cell only without effecting other cell values?