What happens if a deposit isn't paid?
The time is held for as long as you chose. If it isn't paid by then, it opens up again by itself.
Updated
You choose how long an unpaid time is held. If it isn't paid by then, and the client hasn't said they paid, the booking is released, the time is offered to others again, and the client is told why.
A client who says they've paid keeps the time until you check it in your own app.