NTP Services - not keeping sync

[Gremlin]

I have my TOS 5.1.103 system set up to keep time with another local TNAS acting as time server. {This time server is keeping time ok with 'time windows.com'.} However, when using the local time server, time drifts (say) +5 minutes over a few days. A manual update will reset the time ok, so the server appears to be working.

Question 1: how often should the time service update?
Question 2: why is there no option to set the update frequency?

[TMqiky]

At present, there is no option to set the update frequency.
The NTP protocol itself has a built-in mechanism for automatic synchronization of time.
For the problems you encounter, if you use a local time server, time may drift within a few days,
which may be caused by network environment, server load, or other factors. You can check from these aspects.

[Gremlin]

In other words, there is no point in using TNAS as a local time server if you require any degree of accuracy. Thank you.