I had a similar issue, when the NAS shutdown it forgot the time.
I've just send in a reply, it still has to be approved by Synology, so give it a little time:viewtopic.php?f=19&t=47782&e=0
My problem was the battery of the NAS motherboard. It didn't work, so the NAS forgot the time when it shutdown. I returned it to the store for a new NAS.
Hope this might help.