I am just finishing up the installation of a small hydroponic system. I have 7 bato buckets for tomatoes and three rail systems for lettuce. I don't have timers for my nutrient pump. Would it be overkill to run the pump full time?
For lettuce being grown in an NFT system, a constant nutrient flow is fine. We grow our hydroponic lettuce with a constant trickle of nutrient flow 24-7. (But it must be only a trickle if it's a constant flow.)
But for the tomatoes in the Bato buckets (or for lettuce in a growing medium of some sort), I would recommend using a timer. A constant water flow will flood the roots and starve them of oxygen. A plant with waterlogged roots will exhibit symptoms similar to water-starved plants, and will eventually die.