Its not a huge injury. The miniscus is only a layer around the knee, it can fold over on itself which will then cause pain as it rubs against the other parts of the knee. The injury is actually usually caused by overkicking/extension or a sudden twist not an impact injury.
I had the exact thing a few years ago. The scar heals within 4/5 days.
It all depends on whether they 'scoped' out his knee as well to ensure everything was ok - it they did the knee will take longer to heal due to inflammation.
Loads of cold therapy to reduce inflammation. Ice, cyrotherapy, standing in ice baths etc
Back light cycling and swimming after 7 days.
Running within 2 weeks I'd say.