When you complete the check-in process on the app, you will be asked to select a Check-In time. I believe the earliest time available is 11 or 11:30, and it is possible, based on when everyone completes the check-in process, that all may not be able to get the same time. Before COVID, you could show up at any time, but in my experience since then, they do try to adhere to the times you are given. I have seen people show up at the port early, only to have them told to wait outside until their scheduled arrival time. I have not personally done an embarkation in Vancouver since COVID, but I would imagine that it is similar to other ports. My point is, don't expect to show up at 10:15 and get on the ship first thing.