Surely if the rounds been going on one pool for 45 minutes, Then no matter how long the round continues, thats 45 minutes where you are being paid on a PPS. You then earn a few shares from the pool with considerable value. If the round ends within a couple minutes, its not much but you're miners haven't lost much.
If its a few hours, then for the 45 minutes you have been making coins while everyone else here has shares which value is now void.

Now whether 45 minutes is the sweet spot I don't know, and without looking into the maths properly / how much you get per share at a PPS i can't be certain you would earn more, but It seems probable.

Will work it out later. Hopefully you are right and the numbers will prove me wrong!
I mine on a fairly low power system. 40Mhash. If my last share is 30s from the end of the round I seem to get twice as much as if its 2 minutes!