Waiting list when a time slot is sold out

When there's no inventory available for a time slot, allow the customer to sign up to be notified of new availability. Some questions:

• Is it helpful to have this for any timeslot or only if every time slot is sold out? e.g. If Monday at 9 am is sold out, should there be a "sign up to informed of availability"

• Is it helpful to have this only if every timeslot is sold out? e.g. "There is no current availability. Please provide your email to be notified of new availability".

• Should the emails just go into an exportable list to be manually emailed from the merchant's choice of email tool? e.g. Gmail or Mailchimp.

• Should the waiting list be automatically mailed as soon as there's inventory for any time slot? Any other thoughts world?

Idea:

• Notify in the order in which they arrive on the waitlist with a 15-minute (or admin-set) delay or the choice to release to all waitlist members at the same time.