It depeneds on how long the cruise is. there is normally 2 in a weeks cruise or 3 for up to 2 weeks. However, if you don't want dress up on all the nights there are venues were you can have dinner and be in casual clothes. Have a Good Cruise.
NCL is a 'freestyle' cruise so it always your choice how you dress there is no formal dress requirements although it is still a 4* superior cruise so long trousers for men in the evenings etc.
Where can you smoke on board a ncl cruise.