Mine did the same thing last season. I have a bad float that went bad. Once I replace it, it drained fast. If that's not the problem make sure it not the pump or the filter is clogged.
Can you hear the pump cycling? Either float as @Bayrunner suggested or you have a blockage to the pump. Have a look at the sump pump and see if is full or overflowing into the bilge
Answers
Regards,
Ian
The Third “B”
Secretary, Ravena Coeymans Yacht Club
https://www.rcyachtclub.com/