Yes. You just show up when you want to. We actually prefer traditional dining, as we like getting to know new friends. And, it takes more than one meal to connect enough to even begin a friendship. But, we also enjoy the alternate style, too, so it's all good. Just FYI, on the Legend, you can start with traditional, then change to open dining, but not back again. Guess they don't want to confuse the waiters!
P.S. We have sailed the Legend many times and it is one of our favorite ships. If you like sushi, there is a free sushi bar almost every night.