I got to thinking about how time passes in a dungeon as my work hours changed - and changed again. Sleep cycles are strange things. I work overnights 5 days a week and am in bed by 7 am when I return from work, but the two nights that I don't work, my body wants to sleep like a "normal" person. This is with the help of clocks and alarms to keep track of time.
Just how well do adventurers keep track of time in a dungeon or the like? Perhaps by burning torches or lanterns, but that often get's replaced by the light of magic swords and such. How does the spell caster know he spent 8 hours resting and can now memorize new spells? I don't see the party bringing along a water clock just for the occasion ;)
I'm not saying these thoughts keep me awake at night, but they certainly make me think.