I think that's fine! I've had all sorts of commitments that have threatened to screw up my schedule but I managed by switching days off. In fact, I've been alternating my w/o schedule so that I do the workouts on Mon-Wed-Fri one week, and then Tue-Thu-Sat the following week. that's just how it's had to be for me. Just so long as you fit them all in and have at least one day off between the two upper body workouts you should be fine.