Jance gave you some awesome advice and I agree. I'm not sure twice per day once every 5 days is ideal for the posterior chain if you're using axially loaded exercises that have an eccentric component, at least not unless you're VERY weak. The weaker you are at a movement, the more frequently it can be trained because it's less taxing on your recovery. Your routine structure is solid, but I would just spread it out to once every 7 days or once every 10 days, alternating between the 2 routines. If you absolutely HAD to train your back twice per week, I would make sure the second session was very light, high rep stuff like bodyweight 45 degree back extensions, reverse hypers, controlled jefferson curls, etc. Good luck!