you can probably bump the photoperiod up to as long as you want, the rate of uptake is driven by the intensity so if you leave that alone, it should not over-filter. Adjusting the intensity from 25% (halfway) to 50% (knob at 3/4 of max) is where you can fiddle with it a bit. If your bioload is relatively low, you may not need much more intensity, if any. Offhand I would say it would be pretty easy to over-filter a 57g with an L2 on it, so whatever you do, watch the algae for color changes. If it gets a lot lighter and starts to turn yellow, you're pushing the edge. But if you had algae on the rocks, you could still have nutrients to pull out for a while.
New tank uglies - yes, that is a thing! #15 below
http://www.reefkeeping.com/issues/2004-01/eb/