Any watch will do (or even counting consistently), since sub-second accuracy is not required.
AFAIK one time unit is one second, but I rarely used spells with time durations. I did check the timing of Survivors Instinct. With that skill you recover 1 hit point at a rate determined by the skill level. At level 1, with a 'rate of 12' you get a hit point every 12 seconds, etc. This skill isn't very helpful during battles, but is handy to top off your hit points between fights, whenever you head back to base to drop off loot, etc.
I may have time later today to try a couple spells under different rendering methods.
