You count embarkation date as day zero. This is from the Bermuda government website FAQ
12.
How do I count the days for my pre-arrival test? Do I count the hours? If travelling by air, your arrival day in Bermuda is Day 0. If travelling by sea, your departure day is Day 0. The hours are not counted. This means if your flight arrives in Bermuda on a Friday or your ship departs on a Friday, a supervised antigen test done no more than 2 days before would be done on the Wednesday.