Last year my daughter got a minor concussion in a soccer game. Knocked heads with another girl. Not a big hit and she didn't even come out of the game or know she had a concussion until that night.
Long story short is it took her six weeks to get cleared to play. They have you test on a computer and compare your performance to a baseline test you previously took. Some people are back in a week and for some it's months. Everyone seems to be different.