@At404 firstly it depends which one you'd be put on. I was on Tamoxifen for 4yrs pre menopause and had zero side effects honestly. The side effects Ive found are not just the AI but a combination of things, mainly chemo induced menopause, then chemo and the the AI on top. Mostly joint stiffness is what you'd experience and thats what the Oncologist would tell you. I've tried morning and night, makes no difference at all. I also on my Specialists recommendation come off Arimidex for 6 weeks and had to document it but then had to go back on it. I am now switched to Aromasin but honestly pretty much the same. I'd say theyre niggly side effects, not earth shattering that you couldnt live with. It would take quite a few weeks before you'd notice anything.
As I said, I have 6 monthly Prolia injections due to osteoporosis in my lumbar and neck but that was from chemo not the AI. My Oncologist also said, my next bone scan usually you would see an improvement due to Prolia. So that will be interesting.
Like @socoda said if you feel there are too many side effects, just don't take it, you can choose any time you like. It's always up to you, but I honestly wouldn't be panicked about being debilitated completely by it.
Hugs Melinda xo