Generally speaking its always better two split your workouts into two sessions per day. It leads to a better metabolic response, and a better hormone response. Hoping Zir Red or mattsamms chimes in on this one.
Most Olympic athletes will split their training into two sessions per day. Granted that doesn't mean you should do a heavy squat workout then a heavy back workout. Split one workout into two.
However, shoulders and arms tend to be less stress on your body overall so you can do those on the same day no problem.
I say go for it!