When I brewed last night, my yeast starter had been in the refrigerator for 24 hours and it had "a lot" of yeast settled to the bottom.
I am brewing tonight, and my yeast starter has only been in the fridge for 12 hours, and it appears to have roughly half as much yeast as the previous yeast starter settled to the bottom.
I made both starters at the same time from the same DME. The only difference is the yeast and the fact that the yeast starter I'm doing tonight would have been spinning longer.
I've read on the internet that 12 hours in the fridge is more than enough.
My fridge is on the lowest temperature setting -- so cold that water would freeze up if I left it in there (but not cold enough to freeze beer).