What ship are you on? We sailed on Oasis a few weeks ago and didn't do it until we boarded the ship. There was plenty of availability.
No reservations required for anything in the main showroom, only for the Ice Show. It will be performed on at least two separate days, maybe more. It should show up in your Cruise Planner on the website 60 days out. Don't fret if you miss pre-reserving - tickets are available on board or you can just walk in. (Try not to miss it though - it's great!)Liberty of the Seas.
No reservations required for anything in the main showroom, only for the Ice Show. It will be performed on at least two separate days, maybe more. It should show up in your Cruise Planner on the website 60 days out. Don't fret if you miss pre-reserving - tickets are available on board or you can just walk in. (Try not to miss it though - it's great!)