As I remember, the 2317 gets its time from the PBX just like any other phone, but the iteration between checks is not every second. I remember the night of Y2K watching the 2317 in our Data Center turn to Dec 32, 1999 12:00. I was about to panic when it refreshed to the right date. (Was not expecting that!!!) Unplug the phone power supply and see if it updates with the right time.
I do not know if the phone set time updates are configurable, but I do know the more stations you have, the longer it takes for them all to get an updated time stamp.
Hope this helps,
Scott M.