There are ostensibly two lounges set aside for certain guests on IOS as there is for most of the RCI fleet. One is for those in the suites and the other, the Concierge Lounge, is for Diamond and Diamond plus Crown and Anchor members to use. You will have a card key which allows you entrance at most times of the day and you will be able to get snacks and drinks between 5-30pm to 8-30pm. (Yet another reason to have late dining) There are times when there are a large number of Diamond members that another lounge will be made available. Hope that solves your query. ... Ida.
The Diamond Club is on Deck 14, a nice lounge set up and an outside seating area too. Need your card key to enter this room.