First off, thanks so much for your hard work getting the scheduler fixed up, Henning! It's working way better than it ever has.
When using "Add single Slot" in the scheduler, there is no "Email a reminder" drop-down box like when you use "Add Slots." In order to get around the issue, faculty have been using the add multiple slots option to only add one slot. Kind of a pain in the butt but not a deal breaker. Even still, adding a single slot should have that same option to send reminders to people who sign up.