It takes on the average a full 5 days for recovery.
Mixing up the routine shocks the muscles, the problem is the muscles will get used to the mixed up routine. I have heard many different approaches to this, putting them all together, I flat bench
once a week and when I am not gaining, maybe every six weeks, I will either do a high rep work out or switch to DBs for for 1 or 2 weeks. Maybe even going to DBs next week, then to my regular routine the following week, then to a high rep work out the following week, then back to my regular routine. The trick is to learn to listen to your body, Im still trying.