you need three days between back and legs. to be honest 3 days per week is plenty if you know how to train properly. I have made my best gains in the last year just training twice a week. current stats 6' 305lbs. on a five day split if you are training heavy you will not grow to your full potential unless you got freaky genetics. is you wanna be big and strong try this.
monday
legs
squats, box squats, hacks or leg press. pick two
tusday
chest, shouders and tris
flat bench, board presses, side laterals and cable push downs or medium grip declines
thursday
deads and heavy back work. if you gonna do bis this is the day after back work is complete.
cardio and abs on off days if you like.
Guaranteed to grow on this routine.