Mine have to confirm by 10am, or the booking is early then an hour beforehand. I get back from the gym around 8.30-8.45am and switch on my phone, so they have a fair amount of time to text (they can text at 5am if they want to, I just won't see it until 9).
Half hour gaps between, so if somebody faffs about I still have time to change linen/shower/get ready for the next one