Why do my GIO Clock not sync?

I have:
2x GIO
2x NoMad as BackUp for the Console

1x NoMas for control house lights.
This NoMad have i called "Dimmercity".
On Dimmercity runs a SNTP Time Server. (NetTime 3-1 4)
In this TimeServer is allowed, other Computer can get time from this Server

The Cocsole are set get Time from Dimmercity.
But,... the Console don`t do.
The Dimmercvity have two Networkcards.
One only for ETC Net (10.101.91.XXX) the other for Internet and get time from Internet (192.168.1.XXX)
Dosen`t matter on waht IP i set the Concole for get the Time.
After 1-2-3 days the time between Dimmercity and Console are different.

How can i force Console get time only from TimeServer?

(This "fault" is on both Console same)