Feed stability... What is preferred time before the feed breaks down?

It used to be preferable to have feed pellets with a long stability under water, especially if you only feed a couple of times per day, but with new auto feeding systems that feed at much greater frequency, or on demand like the acoustic feeders what would be the ideal stability time? My thought is that if you feed every 10 to 15 minutes, you would want a pellet that lasts that long and no more...? Interested to get some thoughts on this.