I did the leg from Cape May to Fishers Island a number of years ago in mid-May. We had reasonable weather, but it was a run with very light winds. According to my log, we motorsailed for the first 12 hours and then took the sails down and motored another 24 hours. The total distance was 206 nm, which is close to the distance from Cape May to Block Island. Our crew consisted of 3 adult males, which was a good size, especially after our wheelpilot crapped out in the Chesapeake.
Our 35' boat has a waterline length of about 28 ft. Your estimate of 50 hours for a 28' boat is realistic.
For what it's worth, this was part of our 1700 mi delivery trip from Clearwater, FL, that ended in Mystic on the 19th of May that year. We had really good weather for several weeks. We resorted to a harbor of refuge on one occasion in the Chesapeake when the winds hit the upper 30 kt range, but that was a single event and we only lost half a day. My recollection is that we had checked the weather patterns for that time of year and made the decision to go--with no regrets, obviously.