There is no option on the Settings > Maintenance page to activate a schedule; should there be one? (Reminder: I am using the free version, if that makes a difference.) In the Status and Versions section of the Maintenance page, it does say:
Clean Transients February 24, 2017 15:53
However it has said that before with an earlier date, and the date has passed and the transients were not deleted. The date changes, but the transients are not deleted.