It takes twenty minutes a pop. You only have so many minutes in a day/before the next encounter.
Then, the system details The Act. Unless you have huge Constitution, Fortitude, and Charisma, you can't lay in bed all day serving investigators looking to borrow your services to heal, restore spells, or commune to their deity.
I'm working on a Pathfinder version. It will mostly be the same, since Pathfinder is just a more interesting but a bit more underpowered version of 3.5.
That post will include details on The Act. I just hope simply replacing words is enough XD I'll PM it to a mod for review before I post it so I don't take chances.