User-Defind Exception / Format TextBox

I am trying to get a textbox to have a time value of mm:ss. I am trying to make sure that what the user has entered is in the correct format. i.e. If a user enters in 0923 the exception would be thrown. But if 09:23 is entered it would pass through. Below is the code I currently have. I have tried 3 different things and none work. Any help would be appreciated.

Thanks


Try
'If txtRun.Text <> Format(txtRun.Text, "{0,mm:ss}") Then
'If txtRun.Text <> Format("{0:mm:ss}", txtRun.Text) Then
If txtRun.Text <> Format(txtRun.Text, "{0:mm:ss}") Then
Throw New BadTimeException("Please Enter a Correct Time")
End If

Catch BadTimeExceptionParameter As BadTimeException
MessageBox.Show(BadTimeExceptionParameter.Message, "Invalid Time", MessageBoxButtons.OK, MessageBoxIcon.Error)
Exit Sub
End Try

Run = Format("{0:mm:ss}", txtRun.Text)