Curbside Appointment Reminder

Hello, I just installed the curbside module on a 3.3 system, and one thing that our current curbside solution has is the ability to remind the user x minutes before their scheduled pickup time. In theory this helps cut down on no shows.

I think this should be possible to do by using the slot timestamp as the delay field, with a negative delay.

I'm not sure how it would deal with appointments that are rescheduled after the reminder goes out though. Miker suggest that max-delay could handle it.

IRC Discussion from 10/20/2020:
<Stompro> Has anyone worked on a curbside reminder notice yet? I'm thinking it could be close to the confirmation notice, just filtered/delayed on the slot timestamp? But rescheduled pickups might be missed?
<miker> Stompro: I have not, but I agree, it should be doable. not sure if there's a perfect solution for rescheduled appointments that are very near the original, but then, that's kinda like hold-shelf expiration. (though I grant more likely for curbside.) I imagine with some restrictions (have to reschedule at least 24h later or something) you could use max-delay to hide previous notices
<miker> or (new dev) we could cause a reschedule to emit a new event

If anyone has already worked on this, I would like to see what you came up with.

Thanks
Josh