if you are asking about how long linux takes to synchronize to an NTP server, it is only a few minutes. It has a "backoff" setup, so it checks less frequently as, it becomes more stable and gets reliable responses from the NTP server.
It is NOT adjustable, it is built into the NTP code which is part of linux.
You CAN change which NTP servers you use, and, they must be "traceable" to a Stratum 0 or 1 source, for them to be reliable. NTP carries information about where the sync orginally came from... ideally you want it to be an atomic clock, such as time.nist.gov, or one of the many other atomic clocks available via the internet.
Mitch
AVAYA Certified Expert