NTP Server Online Tester
This tool is useful to check if a given Network Time Protocol server is reachable over the internet using IPv4 and IPv6 connectivity.
It is also useful for knowing the resulting offset using the exact time of 1a.ncomputers.org stratum 2 NTP public server.
ntpdate -q to perform a time synchronization query which works for linux servers, windows servers, etc.
Recommended for web hosting and server admins:
How to join your linux server to the NTP pool project
How to query and test an NTP server using ntpdate