Its quite hard to avoid losing track of time with the timers on the 8052, because I have always found that there is enough uncertainty to cause slow drift.

Better to use a RAM with a clock built in - Dallas semiconductor are real good for that, or their DS5000 8031 with built in RTC which is nice, but lacks the full 8052 architecture (no Timer 2). On the plus side though it has a really nice serial boot-strap loader.

Steve