Wait a sec, does that mean anyone who hasn’t filed yet can’t run ?
No, not even close. Each state is different, but prospective candidates probably start turning into pumpkins sometime in early December, or later depending on when the state's primary is actually held.
There is no federal deadline to announce a candidacy. All that matters is getting on the ballot in the requisite number of states.
No, if that were what it meant, it would be the REVERSE of the time when Fox would axe them. It's probably an internal Fox deadline that says "You must decide by May 1 that you aren't going to run this cycle or you can no longer appear as a commentator on Fox till you DO commit to staying out." Wonder if any of the networks with greater actual levels of bias, but on the acceptable side, worry about crap like this.
I believe Clinton entered the race in November.