How long until you void a restaurant booking?

I was at a lovely open air Balinese restaurant overlooking Double-Six Beach when we desired a prime position table in the open air section of the restaurant - the key words here being open air. As the people seated close to us were chain smoking and blowing their dirty smoke in our direction - so we requested to move.

The restaurant staff dutifully informed us the table we requested in fresh air was unavailable as they had a standing reservation - fair enough. We ended up at a less attractive table but this is still better than breathing dirty air so no complaints. What I did notice as the table where we were unable to sit was still empty, now more than an hour had passed since the time on the reserved sign had lapsed and I asked myself, how long can you hold a table?

It is unfair to the restaurant, it is unfair to diners and it is just rude. You can be a little late, that happens but any more than 15 minutes and either a phone call is made or the booking is relinquished after 30 minutes as diners are inconvenienced and the restaurant is denied income from the table. In this instance, we could have been seated with an excellent view of the beach and when we left the table was still vacant. So while I don't know if this reservation ever filled, these people should be more respectful to diners and the restaurant.