...nope, 40 sec works for me across all counts. I will add that as an extreme exception, the other day I burned a 40-mesh and increased the time a bit, only because the coating was quite a bit thicker than the standard. Still, I think I only went to 50sec and the image was just fine.
...Now granted, I'm not the guy breaking out the microscopes, densitonomers and what have you. What I DO know is that, 40 seconds, paired with the proper mesh selection, gives me nice, durable, screens with halftones better than I have ever achieved before with fluorescent units. And, in a fraction of the time.