I can usually drop players when I wake up the next day... ~6:30am... not an official answer but thats the earliest I've tried.
QB: T. Green, Grossman, Garrard
RB: L. Johnson, Westbrook, Foster, T Henry, Jones-Drew, Buckhalter
WR: Fitzgerald, Chambers, A. Johnson, T. Glenn
TE: Cooley, Witten
DP: R. Lewis, Polamalu, Trotter, Brooking