Right shoulder replacement, 3/2016. Doc insisted on 3 months off the road, but he was OK with my getting on a trainer at 6 weeks, IIRC. His fear was that I'd rotate my shoulder more than 90 degrees before the muscle knit - if the big muscle ('something scapularis'?) in the front of the shoulder split, it's apparently hell to pull it back together.
My first ride was 3 months to the day after surgery. The surgery affected my riding positively - no pain.
Note that I did the PT exercises pretty religiously, and I had a very good PT (gentle and sensitive; she pushed me hard but not too hard). My pain interfered with my sleep, and the surgeon I was working with was 2nd on the list my PT gave me. (The top guy was at a hospital known for rigidity (they, not my GP, had to do the pre-op exam, for example) and poor customer service (multi-hour waits to see the doc with whom you have an appt.), so I wanted to use the guy close to home.) You probably want a surgeon who does shoulder replacement pretty regularly.
Best of luck.