I start stirring the day after I add the yeast, so that the yeast kind of find their way around first. There really isn't any reason that I know of to wait a day, though- that's just what I do. If I'm making a wine that makes a thick "cap", I stir twice a day until it reaches about 1.020, then I rack to secondary.
Broken Leg Brewery
Giving beer a leg to stand on since 2006