Strange that the clock drifts so much.. PC clocks are suffering from the original PC design I believe, the PC came without a battery so the first thing that happened when you booted (from floppy..) was that you were asked for the current time. So no need to design for an accurate clock, right? And besides, the actual DOS counter couldn't count accurately to 24 hours. So it drifted.
On the other hand, the clocks in both of my old (well, old design by now) Palm Tungsten T3's are very accurate.. strange that the 770 should have a problem. On the other hand, the T3's clock can be synchronized with my BlueTooth GPS time (very accurate!), that should be easy to get working on a 770 as well I should think.