Your hubs firmware needs to be at least 2.1.5 then you can use this community created driver
to choose your own NTP server, by default it will try to contact a specific pool on the internet but if it cannot access the internet for a while it seems to stop trying until rebooted and if it cannot connect to the internet when the DB backup is performed each night on on reboot then it really will get out of sync like days or more. If you have a Windows machine always running on your network that NTP driver works great once you setup an NTP server service.
