Can i exit the Shanghai airport if my next transit flight is 5 hours away?

Yes, you can get out of the airport.
Near the airport, there is no place to hang around and the time is so short to travel to the city downtown area, so it is suggested to stay in the airport.
If you do not want to stay in the airport, it is suggested to take the maglve to reach Longyang Road Station area where you can find supermarket or so. The maglev takes about 8 to 12 minutes to reach Longyang Road.