NCLCR

I'll be sailing on a 5 night cruise on Mariner of the Seas and would like to know (if there is an answer): 1. Is there always a lobster night in the MDR on a 5 night cruise? 2. If so, is it always on formal night? 3. If so, is there a way to tell what day will be formal night prior to asking someone once I get on the ship? Mariner Cruises since the shut down have only been 3 or 4 night so there isn't a recent cruise compass to check. This usually does not matter to me, however, this will be my mother's first cruise, she likes lobster, and this is the first time I have purchased the unlimited dining package. I am just trying to make my questions/reservations when I first get on the ship as efficient as possible.