Hi,
For example if a clock update has to happen at 1 second intervals, how does it matter if it happens at 999 ms or 1001 ms
The result is 3.6 seconds per hour - very bad for watch clock :)
In serious, I agree with Erik: do things simple and they be easy. Anyway, RTOS is not real multitasking system; it just uses time-quanta model. Usage of timers of 51 is enough to do it even in pure ASM.
Good days!