We’re on the same cruise on June 22 cruise so I will report back.
However, we did a similar cruise on summit about 10 years ago where it had the overnight in Venice (sigh, yes actual Venice but we now all suffer for MSCs failure).
Then, we arrived quite late first night due to flight delays but there weren’t any concerns. Celebrity told us that the ship essentially acts like your hotel for overnights. You’re free to come and go as you please or even stay overnight off site. I’d doubt that’s changed!