There seems to be a wide variation as to when they drop em.(here in Pa at least) I shot a monster of a doe several years back on the last day of doe season only to discover that my "doe" had empty bases in her head that were almost 1 1/4 inches across. The deer seemed to be in fine health too so who knows why he dropped so early. I have buck near my house that have dropped their horns, and others that havent.
I think in general, late Feb thru march would be the best times to shed hunt since all buck should have dropped their antlers by then.