I've designed the PH3 program around very specific calculations in order to yield maximum results, and you don't get to play with those numbers. I guarantee the science and research that went into this program are much more reliable than any guesses or tweaks you might want to add.
That said, you do have some wiggle room when it comes to the schedule. If you can't budget enough time in the gym today to complete both the squats and the leg workout, do some of it tomorrow.
3 sets of 5 reps