I switched from 1 light to 2 lights to reduce my time from 19:30 to 9:30 but I am using velum paper doubled up to get my stencil dark and I needed to add time for the uv to penetrate the opaque paper.
What I found made for crisper lines on fine detail was to use the 1.5 times each inch of the graphic to set your distance from screen surface worked perfect and checking your light pattern to see if the overlap area from the two lights cover the entire graphic is a must since the uv only doubles in the overlap area effectively. Much like you check your high-low beams on your car just see what the light pattern looks like on a wall at different distances and do some simple math for the overlap. I had to set my lights at 20 inchs away with the lights on thirds below, not side by side, to get my coverage right. One light was to slow and the outer edges of the stencil are actually farther away since the light has to travel farther, this was leaving some soft spots washing out on the edges if the center was dead on and not washing out evenly in the center if the edges were right, I was doing some very fine detail, two lights solved this issue once I spread them apart to evenly cover the surface. A bank of florescent lights does this nicely also but with the sharp edges I needed I used point lights. Conceder metal halide lights they have even better uv output and could also cut down the time and are also point lights if you want to do very fine detail. I also switched from a diazo emulsion to a dual cure to hold the edges of the detail on the 110 mesh screens but using a 156 up to a 230 would also work for the fines detail but be sure and thin your whites or you might have problems with that mesh size.
Hope this helps, I just went through this myself the last few days getting everything right, reclaimed a bunch of screens that didn't work out till I got it right. Hope my pain saves someone else the time and effort.