Can someone let me know if I am missing something with my workout? I am incredibly weak for a man (24 years old 5'7). I like the idea and workout of doing SL 5x5 or similar, but everything says it takes 45 minutes. Then I read about a guy taking 3 hours, but it takes me 15-20 minutes! I downloaded SL5x5 app, but I didn't see what I was missing.

1 set of 5 takes about 1 minute, I jump up go to the next without breaks. To let my arms rest I throw in 5x5 leg exercises or crunches between each set. My other concern is weight. I thought you were supposed to lift about 90% of your max (about 180 max for 1 benchpress) so I am doing 5 at 160. SL5X5 recommended I do sets at like 80-90 pounds.