Your customer would like to limit access to the online content to one-time slot on...

In the time slot of the class, check "Allow access to online content" during this time slot.

In the item, set "Unregistered User Can Access Online Content" to No.

In the item, set "Content available only during specified time slot of a class" to On.

In the class, uncheck the "Online Access" checkbox for the time slot on the last day.

In the user entity, uncheck the "User has access to the online items" checkbox on the Content Status tab.