If you have an event date with multiple time slots and have activated a waitlist, your ticket buyers will automatically be shown the option to sign up to the waitlist for all time slots. This is useful when a ticket buyer knows which day they'd like to buy tickets for, but is flexible on the time.
How to sign up customers to a waitlist for all time slots
When your ticket buyers check the box called 'Notify me about availability for any occurrence on this date', their email will appear on the waitlist for every occurrence on their selected date.
When tickets become available, you can send an email broadcast to notify all waitlist sign-ups, which will include people who wanted to book for that specific time slot, or for all times that day.