Rene,

If you want all eight LED and timers to operate *independently* then use eight different bytes in ram to count down the seconds.

The 8051 TIMER would be used to decrement all eight bytes in RAM. After that, a routine examines it of the eight bytes in RAM to see if any require their associated LED to change.

If any key selects to discountinue a timer, you just change its byte in ram among the eight. If would be wise to use a flag to indicate which of the eight timers (eight bytes in ram) is active.

If you use flags to select which timers are active, when your 8051 TIMER initiates decrementing the eight bytes in RAM, it can use the flags to ignore byte timers that are discontinued.

Hope that helps.
aka j