We were on the inside passage to Alaska. Ketchikan, Skagway and Juneau.
Next time we plan to go to Denli,etc. and maybe the train to the interior.
The formal nights are usually on the second night while at sea, and on the 5th night cruise. If it is 10 day the formal days are different. You could ask someone who has been on longer cruises.
Hope this has been some help