All reviews are, by design, linked to scheduled tasks for both the Admins and the learners. If a review has not been scheduled, it will automatically create the schedule/tasks at the time that the review is started.
There is no way to turn off scheduling for a review but there is an option to pre-schedule it as "All Day" instead of at a specific time.
FAQ: Is there a way to add a review without the system also scheduling the review meeting?
Brian Leahy