If you are jumping like a complete maniac on every tack 90 minutes is probably good.
I doubt many people can go completely apesh!t for 6 hours straight.
As you get more experienced you will use less effort, and probably be more selective with your jumps, and other "maniac like activities".
i.e. Only jumping when you are doing warp speed, have a perfect kicker, on a gust, and the water is blue enough. vs New guy who is SO excited and jumps every time he sees more than 4mm of chop