I'm a bit surprised. It's not common to do rotator cuff surgery on a person your age, and with the arthritis history.
However, is surgery was determined as necessary, then it is likely the only treatment that will reduce pain and/or return function.
No one, except possibly your surgeon, can give you recovery estimates. Again, your age is the biggest factor and the complication of your arthritis.
As with any soft tissue surgery, the surgery itself is not the biggest factor in success. The success will be primarily a result of your rehab and effort to regain range of motion and function.
I had rotator cuff surgery in 2009. It took 6 weeks to heal and going to theropy 3 days a week. My doctor warned me before hand that the tear was really bad and he might not be able to fix it. To me, it wasn't painful at all. I was told that once my arm became unfrozen (they freeze your whole arm for this ) that I'd be in a lot of pain, but I wasn't. The repaired arm lasted a few weeks and then tore again but the doctor said my next step would be a shoulder replacement so I haven't done anything about it. In 2009 I was still working and needed my arms but now I'm retired and I just learn to live with it. Over the years I've had both knees and one shoulder operated on and they are all back to square one. Like I said, just accept it and move on. My body isn't 30 years old anymore and can jump back to brand new again.