> Means user can set 10:00 = ON, and
> 11:00 = OFF again 12:30 = ON and 13:00
> = OFF, and so on. so user can turn
> ON/OFF several times in 24hours span.

Where's the problem? You just need to have an array of ON/OFF time structures and compare current time to every structure. Somewhere you also should have a byte indicating how much structures are in this array -- the comparison can be implemented then as a simple loop.
This is meant for one output.
The comparison may be as follows: While current time lies within the interval specified in a structure, the output should be asserted (and otherwise deasserted).

No matter in C or asm it is implemented. C looks better though :)
Good luck,
==
Tomas