My first experience with hydroponics was manually dipping gallon jugs filled with lava rock into a bucket of nutrient solution and letting drain immediately for three times a day. It did a fine job on the plants but was a pain...

I suppose it depends on what growing media you're using, how long it retains moisture and the type of plant and its water/nutrient requirements.

To conserve energy, start with the least amount needed and let your plants tell you what they need. If two minutes doesn't seem enough then bump it up a bit till you see the results you're looking for. So many variables among systems, plants, temperature...

I am letting my system run for five minutes with hydroton clay pebbles as the growing medium, because that's how long it takes to flood to the overfill level. However I have been reading something about flooding long enough such that 130% of your nutrient solution is circulated, in order to provide less nutrient salt buildup and better circulation. If that's the case I need to let it run a little bit longer... not sure yet.

As far as water frequency, I have heard that it is best to time watering increments so that you water just as everything starts to air out again - thus taking advantage of all that oxygen around the roots in the mean time in between floods. However again, I am still figuring all this out myself. My plants seem to be dong well though so far.

so i understand that

1- it is good to let the flood last longer to let the nutrient solution circulating and therefore avoiding salt build up
2- a flood allow the root to eat and breath as well because the air/02 is renewed when the water drain.

so i guess having the flood running for 10 min (2min to flood at max) is good enough, right ?

Yea I'd think 10 mins is ok every 3 or four hours, perhaps even a longer interval than that. The flood interval is something I think I will be playing with a good bit too because it's different for each system and environment you are in. You want the medium to *almost* dry out, then flood again, that's what I"ve understood so far. That takes some experience, I think, to really get it optimal, but I'd think you're ok where you are starting at.