Is the 645 connected to a ISP modem of any sorts or to a wall out let?
Yes. I am connected to what is called a "miniWan" which is connected to a wireless (800 MHZ) receiver on roof. I live in bush!
Need to find out what kind of ISP modem services you have.
It is like DSL in that it is PPPOE.
If the NTP server is set up on the 645, it should get time if power is lost and it comes back on.
It is setup this way and most of the time it does sync time as it should. Just sometimes it does not and I am online browsing so there is no reason it didn't. I can log into router and force it to sync and it does. Just wondered if you have seen this behaviour before or not.