Timeout for appointment confirmation

Hi, we are having a growing issue with clients phoning us up, asking for a booking and then not turning up but not confirming their appointment, often the same day. What we have started saying for same-day appointments is that they have say 20 minutes to confirm their appointment, but presently that does not time out or expire, and is reliant on having the time to go back to it. Like longer-term bookings, we can manually go through them and 'ask client to confirm' but some form of timeout option would help a great deal. Ideally, as well as the 'ask client to confirm' option a selection of timescales eg 20 mins, 1 hour, 4 hours, 1 day etc etc. Alternatively the current 'ask client to confirm' would automatically cancel unconfirmed appointments at a set time (eg 2 days) prior.