I suffered a torn MCL & medial meniscus tear a couple of years ago… went to a sports physio straight away (by-passed the GP refereral) and did the recommended exercises & self-treatment religiously.
Back on the road bike within a couple of weeks and off-road within a month or so. Still try and do the recommended balance board exercises & stretching to reduce chances of further damage and avoid having to have surgery later (damaged MCL can seemingly result in ACL problems later due to joint instability).
All depends really on how bad the tear is and more importantly (apparently) how much small tissue damage was done by the subsequent swelling. I was lucky and got an ice compress on mine quite quickly.
Can't recommend going to see a quality sports physio strongly enough!