I called Celebrity for our cruise in Vancouver and they told me to board at 1PM. When we got to the ship, we found out that many people arrived at 11:30AM and were allowed on the ship.
Don't forget to pick up the tourist coupon books at the dock. You will not see them on the cruise or in the towns you visit. We each have free "gold" vials, cans of salmon, rain ponchos, jerky and used the coupons to get many things that were only discounted with the coupons. We felt very happy to use these coupons and spoke to many people who also used them.