I believe there is a bug in the software that causes time change after syncing. If you have itunes running, just Make sure you EXIT itunes before syncing, that should solve the problem.
Make sure your time is correct on whichever computer your syncing with. I have found that if the time is incorrect on my pc, my ipods time will change as well
My 2G touch also suffers from this bug. I'll sync it up and then when I come to use, I notice that the time is out by an hour or two usually. Nothing major, but will be glad when it's fixed, saving me having to change it manually.