Not sure how the Graham link reads, espn is blocked here at work. But this is from the Buffalo News:
The National Football League does not have strict guidelines when dealing with concussions, unlike the National Hockey League. In the NHL, players are strongly urged to be symptom-free for seven days before practicing. The NFL has no such time minimums for head injuries but recommends players are asymptomatic before returning to play. The decision is left to medical staffs of each team.
On a side note, I can't believe there has not been one "I had a concussion in high school and yada, yada, yada" posts yet.