(Alternative to the app)
While playing trivia, I think we saw the time for Happy Hour listed on the menu in the plastic stand in our table. That, or the server mentioned it.
This is so different than on land - the bars are open / unlocked most of the time. You can look on the table for the menu. If one is around, you can ask the staff for the info. You will be walking by them all the time.
This is what I forget about the app: if you want to see more information - like a different category (Dining, activities, …) the categories are written above the list of events. Swipe that area left and right to get more categories.