For the original post if your going to do this I would suggest doing two 1 gallon batches from the same mash and be sure to add the exact same amount of yeast. If you just do one 1 gallon batch there's to many variables that could effect the out come. Mash efficiency, mash temp, quality and freshness of grains used, ferment temp, yeast health. To name a few. So how would you really know if there was a difference from the boil length if you couldn't factor the variables out?