Shewhobikes,
I'm so very sorry. I had the rotator cuff surgery on my R shoulder in '06. What you've been told about your rehab is pretty much exactly what I went thru. Surgery was early May. My 1st bike ride was, I think, August. What Kiwi said was correct. Wear your sling 24/7, showers the only time you take it off. This prevents that arm from pushing, pulling or lifting. My ortho said if I didn't rest in those first critical wks. I'd possibly pull out the anchors. I got a shoulder specialist PT rx. from the ortho.,started PT before the surg., went 2X a wk. @ first, & did the exercises religiously, sometimes 2X/day....do whatev your PT recommends. My PT also told me not to stop my weights, that doing them on my good side conferred a 10% benefit in strength to my healing R side. Then after some wks. I asked my spin instructor if he'd allow me to the class wearing a sling...so I did that. Very carefully. When I got the ok to do charity rides & the like (in aug.) I purposely stayed WAY back at the start. To fall off the bike would have been potentially disastrous. Also, I could not do the full 40 mi....my shoulder began to ache & I did NOT push it. Got my H to pick me up.
Being careful but being active, doing the PT, being patient...that's what it takes...after 1 yr. I had to get an independent eval. of my shoulder function (insurance BS) & that ortho. told me he'd never seen such a good outcome from that surgery as I'd had.
Good luck to you!!
Sooz