I'll normally run the stir plate at a speed that allows a small funnel (vortex) to form in the middle, then back it off just a hair until that vortex is just a low spot (1/2 an inch to 1 inch deep) in the center but not quite a full vortex.
It really only takes 24 to 36 hours to fully ferment out, but I'll typically let it spin for a couple of days, then crash it in the fridge for another day or two - depending on how far away brew day is - and decant the spent wort off the yeast cake come brew day, leaving just a little wort on the cake - let it come up to pitching temp, then pitch.
I'm simplifying quite a bit here, and making some assumptions that, if you're making starters, you have a fairly advanced knowledge of brewing already.
