=IF(A1<=TIMEVALUE("3:00 PM"),"RB",FM")
Option Explicit
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Cells.Count > 1 Then Exit Sub
Dim cellA As Range
If Not Application.Intersect(Me.Range("K:K"), Target) Is Nothing Then
Set cellA = Me.Cells(Target.Row, "A")
Select Case Hour(cellA.Value)
Case Is > Hour("3:00:00PM")
Target.Value = "FM"
Case Is < Hour("3:00:00PM")
Target.Value = "RB"
End Select
End If
End Sub