45 minutes - 1 hour
LH Fan on my MBP had become a bit noisy - especially in cooler environments. I do astrophotography as a hobby, so am often out in cold weather. Tried blowing the dust out - no good. Went to Mac forums (apple.com site), and folks said to replace the fan.
I'd been inside the case before - to upgrade the hard drive, so getting in was pretty easy. I originally ordered the wrong fan (so many versions of MBP's). iFixit was very understanding. They accepted the wrong part and sent the proper part. Repair was pretty easy - no more than intermediate difficulty (not 'difficult' as indicated in the instructions). Laptop is now as quiet as the day I bought it. Back to imaging
Double check with iFixit before ordering the part. When I got it wrong, I sent info from 'about this mac' (apple menu), and they immediately steered me to the proper part.