I just personally have to disagree with the 40 minute rule - it is just too long.
I don't see why a person should have the right to claim any chair (and some are far better located than others) and then get up and walk away from from the pool area entirely for 40 minutes or even longer anytime the feel like it.
That just makes no sense to me. If you leave the pool area you are done with that activity as far as I am concerned.
Now - if you have relatives still there that is different - under my system they can hold up your card for you and vouch that someone in your group is still in the vicinity. Then you keep your chair. (Carnival's system did not address this issue).
What I want to stop are the people who show up for just a minute and claim two chairs and then leave. They should not have the right to even 40 minutes - I only gave them 15 in consideration for people who insist on using their own cabin restroom or want to retrieve a book.
But I see no valid reason why a person should be able to keep a chair all day, and all he has to do is show up every 40 minutes. My system allows tracking of people who leave, and at 15 minutes people are not likely to keep coming back just to "renew" the ownership.
The main thing is that deck chairs are not like any other seating - they are typically used as a base for pool activities. But if the good chairs are taken then other people are out of luck. Why should someone who wants to sunbathe at the pool have to wait 40 minutes for a chair while that person with the ideal chair in is the buffet eating an entire meal?
They have left the pool area for a substantial period of time - give up the chair.