As far as I recall: set dining times and reasonably formal. The buffet of course is casual each evening and is drop-in.
Expect 2 formal nights on a 7 night cruise so smart casual is hardly the compliant dress code. The main dining room is 2 sittings at set times. NCL is the freestyle line both in dining & dress.....Wilba.
On splendour of the seas smart casual is accepted. Its a very nice ship I like it alot. Caroline/Norway.