The Sherwood computers have an issue with not keeping an accurate count of time of day. My Profile, my friend's profile, my friend's Genesis brand Profile, my other friend's Wisdom 2: they all don't keep track of time-of-day after several ONs & OFF's from the computer. Eventually they become a few minutes off. Mine's likes to set a few minutes faster.
If not corrected you can eventually be 30mins off from the actual time.
Dive time still holds up though. It's only when the computer is turned back on from sleep that the clock fluctuates.
The depth thing you don't have to worry about. Mine was always 3ft away from my school's Oceanic Veo's. But a pressure test showed that mine was in fact spot on. Different brands of computers will read different depths within reason; it has to do with the depth sensor, not every manufacturer uses the same one I guess.