Do you have practical programming?
It goes into some depth as to why 20 reps is no good for strength training. Sure you want volume on day 1. But You want it to be at fairly heavy weights.
5 sets of 5 is 25 reps. And you can probably do it with 90percent of your 1rm. For 20 reps, you would probably have to use 50 percent and I doubt you'd have enough steam to do more than one set.
It would just train endurance, not the right kind of adaptation to help you hit 1-5RM's on Day 3.