Since I don't have your field data to work with, I tested as
Code:
Sub testExpression()
'IIf((Format([TimeOut]-[TimeIn]*24,"Short Time")=>"6:30",
'(Format([TimeOut]-[TimeIn]*24,"Short Time")-"00:30",
'(Format([TimeOut]-[TimeIn]*24,"Short Time"))
Dim TimeOut As Date, TimeIn As Date
TimeIn = Format("07:00", "short time")
TimeOut = Format("15:30", "short time")
Debug.Print "time in: "; TimeIn & "; " & "time out: " & TimeOut
Debug.Print Format(TimeOut - TimeIn * 24, "short time")
If Format(TimeOut - TimeIn * 24, "short time") >= Format("06:30", "short time") Then
MsgBox "True"
Else
MsgBox "false"
End If
End Sub
and it seems to work. I also wrapped your comparison values (e.g. 06:30) in the format function to ensure text comparisons ("06:30") weren't being made.