This little macro will do the same thing:

Private Sub Worksheet_Change(ByVal Target As Range)
Dim s As String

If Intersect(Target, Range("G16")) Is Nothing Then
Exit Sub
End If

s = Target.NumberFormat
If InStr(1, s, ":") 0 Then
Application.EnableEvents = False
Target.Clear
Target.Select
Application.EnableEvents = True
MsgBox ("Times not allowed")
End If
End Sub

This sample checks entries in cell G16.

If the user types an entry that Excel recognizes as a time, Excel will
change the format from General to a time-style format. The macro looks for a
colon in the cell format and responds accordingly.

If text is entered rather than time:

HELLO:WORLD

the macro will allow it.
--
Gary''s Student - gsnu200730