Did you configure a data/time group? If not you might need to configure a date/time group and make sure the phone are using that. These phones get their time from callmanager, but by default they will show UTC time unless they have a timezone reference. If you are positive the phones are using the same device pool and same date/time group, then perhaps you have a phone load issue. You might want to pull down the latest firmware for the 7960 phones. I just upgraded a customer last week to 7.1(2) CUCM, and put the latest device packs on the phones - lots of 7960 and 40s. I didn't have any issues with the time.