How the waitlist fills a cancellation

Adding a patient to the list

Four things go on an entry, and each of them narrows what the patient will be offered:

The service they are waiting for. Matching is exact — somebody waiting for an initial assessment is never offered a follow-up slot.
A practitioner, or nobody in particular. Naming one means they will only be offered that person's cancellations. Leaving it blank means anybody's.
The dates they can do, from and to, inclusive, read as the clinic's own calendar days.
Mornings, afternoons, or any. Mornings means before midday; afternoons means midday onwards.

Patients can add themselves from the booking page too, if the clinic has that switched on — usually when they searched for a time and nothing suited.

What happens when a booking is cancelled

Orla first asks whether the cancellation is worth offering at all. A slot less than 90 minutes away is not offered — it goes quietly back to public availability instead. Nobody drops everything and crosses town in an hour, and an offer nobody can take is just an annoying text.

If it qualifies, everybody matching is ranked and the top of the ranking is texted at the same time — up to five people by default.

Why several at once, and not one at a time

Because one at a time loses the hour. If each person gets 30 minutes to reply before the next is asked, then three people who would all have said yes hear nothing until the slot is gone.

Offering the batch simultaneously and letting the first click win fills the slot in minutes instead of hours.

The order

Patients who asked for that practitioner by name rank above patients who said anyone would do. They have been waiting for that person.
Then longest waiting. Among people with an equal claim, the entry that has been on the list longest is offered first.

To change who gets offered first, change the entries — a patient who removes their practitioner preference widens what they will be offered but drops below those who named that clinician for their slots.

What the patient receives

An SMS naming the service, the date and the time, with a link that books it. The link is signed, works only for that patient and that offer, and stops working when the offer expires.

How long the offer lasts

30 minutes by default, and the clinic can change it. If nobody claims in that window, the next group down the ranking is offered the same slot, with everybody who has already had their chance excluded.

When two people accept at once

The first click wins and the second person is told immediately that it has gone.

This is decided by a single conditional write in the database — the slot is claimed only if nobody has claimed it — rather than in application code, so two people tapping in the same second cannot both be told yes. Nobody is ever booked into a slot that no longer exists.

Booking from the list by hand

The desk does not have to wait for a cancellation. If somebody rings and there is a gap on Thursday, open the waitlist and book them straight from their entry: service, practitioner and preference are already recorded, so nothing is retyped.

Their entry is marked claimed rather than removed, so the list can show that waiting worked.

The list keeps itself tidy

An entry whose last date has passed can never match again, so it retires itself, using the clinic's own calendar day rather than UTC. A waitlist that is mostly people who stopped waiting months ago is a list the desk stops trusting — and trusting the list is the whole point of having one.