If his pink eye is caused by certain bacteria or viruses, the infected person can be contagious for several days to several weeks or even more. Since pink eyes caused by infectious conjunctivitis can be highly contagious in environments, you'd better stay away from him till the condition is resolved. In fact, It is usually takes three to seven days till the obvious symptoms of pink eye disappear. As long as the obvious symptoms fade away, you can play with him.
Pinlk eye can be contegious within 24 hours. It can't be contagious 24 hours after you start the drops. Generally speaking, pink eye can go away itself within 24 hours to 48 hours. During this period of time, you should often wash your hands clean and keep the things around you clean. Don't rub your pink eye, either. If it is serious, you should go to see a doctor as soon as possible. The doctor will treat your pink eye.