I think it's all subjective, but I like 5 - 10 minute intervals myself.... I fear that on a "short" interval you end up getting too much of a tennis-match effect in the tank. A few minutes on, a few minutes off, creates a good chaotic motion.
Also, I REALLY like hitting powerhead streams off of stuff to create chaos. I have two 3/4" outlets pointing straight forward so they hit the front glass and cause a "roll under" effect of the water. But, since they are only 8" apart, they also hit each other and create a really nice disturbance pattern with upwells and downdrafts that seems to "mix and swirl" the food as it hits the stream.
I like art in the water... not just flow... but then, I'm really spoiled (and anal) about how things get set up.....