Saturday's WSFS meeting is in a 4-hour block. (the previous two days are 3 hours.) This means that the Business Meeting will convene on Saturday at 10:00 to take up Site Selection business, which will be the announcement of the official results and the initial presentation from the 2019 Worldcon, followed by Question Time for the 2018 Worldcon. If there is time (and there may not be), there will be a short Question Time for bidders for 2020. We plan to recess then until 11:00 for the Worldcon Chairs Photo Shoot.
Substantive business other than Site Selection will commence when the meeting reconvenes at 11:00, and will run until 13:45 (or sooner if we somehow manage to finish everything, which I doubt). There is a final session scheduled on Sunday from 10:00 to 15:00.
If you are coming to the Business Meeting in Helsinki and have no interest in either Site Selection or the Worldcon Chairs Photo Shoot, you can sleep in an extra hour on Saturday morning.