Evenglare
Adventurer
Why wouldn't you do it, with the way spell casting works.
I figured the reason not to do it was obvious, but I'll spell it out. 20 minute days completely destroy the pace of an adventure. The ability of the caster should be to ration his spells before the day is over and then rest, which is the intention of the game ,they didn't design the spell system to be exploited as in the 20 minute dungeon.