We are sailing on the Symphony May 31st. I had the same issue when I tried to book 150 Central Park in early March. I put a call in to Royal and was advised to go to 150 when we board and they will be able to give me a time later then 5 pm.
I also was able to get this time for same cruise date and ship. I checked in on app which was a bit glitchy so i had to sign in and out several times. I guess it was about 12:15am when it finally worked.