I have worked in hospitality all my life, now retired. In my experience since the early 1970's we never, ever turned away a guest. It was up to the guest to not wait for a table. We stayed open as long as it took to seat all those waiting, even after midnight on very busy nights.
We did book up solid ahead, but always kept a callback waitlist for no shows. Once a waitlist was called back, we took credit card numbers to confirm the reservation, and applied it as credit to the final bill. Seating time was never guaranteed, only that you would get seated. That allowed for walkups to be seated before the waitlist reservation showed up. We never held tables longer than 15 minutes, and that was a policy that never was broken, except for regulars. The 15 minute policy allowed for either walk ups, or early arrival reservations to be seated. Get them in, and get them out. Once a new guest can't get a seat, they usually never come back.