The start date entered for Comp Review doesn't drive any notifications - it's typically your estimated date on when Comp Reviewers will receive access to Kamsa to start entering pay decisions.
Note that the End Date you enter only impacts what's in the email notifications they'd get to remind them of the due date; However, after that “End Date” they won't get blocked from accessing Kamsa (until the Admin approve/close out the Comp Review or the Admin goes into User Management and intentionally disable their access).