A form consisting of from time and to time i need to give validation for theses 2 fields as time (from time & to time in hr:min:ss) how to give such validation so that user will enter only numbers ab=nd withinn hr: min: sec

Try :

Dim regTime As New System.Text.RegularExpressions.Regex("^([0-1][0-9]|[2][0-3]):([0-5][0-9]):([0-5][0-9])$")
Dim t1 As String = "25:12:12"
Dim t2 As String = "12:45:34"
Dim t3 As String = "01:12:92"