If it's ShB hunt monsters then I agree that if you snooze you lose.

But ARR and HW hunts are dead.
You could solo ARR a ranks back in SB and the same is probably true for HW a ranks now too, and if you can't solo ARR s ranks yet then come back a few raid updates later and check again.

They may be free for all, but I'm damn sure they never intended for them to be solo'd.