Yes, there is an exception that is thrown if the NTP server is offline. If you look at the MSDN documentation for
Socekt.Connect[
^], you will see the list of exceptions that it could throw.
If my memory serves me correctly, you should get a SocketException with the details being connection timed out. The easiest way to test this is to modify your host file to point asia.pool.ntp.org to 127.0.0.1 so that it tries to use your local machine to pull the time information. This will simulate them being offline.