You can easily test the availability of an NTP server by using ntpdate. This utility is a command line utility which performs a one-time time sync to the specified NTP server but it can also be used to query the time without setting it by using the -q parameter:

$ ntpdate -q 10.30.0.1
server 10.30.0.1, stratum 4, offset 0.001217, delay 0.04170
 8 Jan 10:19:36 ntpdate[2376]: adjust time server 10.30.0.1 offset 0.001217 sec