Several of mine have lived outside full time for weeks. But I have fully screened balconies, so they have a very large 10' x 10'+ "cage" to move around in. If the temperatures are not too high or too low, then they can be out there as long as they want. And you can mist them throughout the day to keep them hydrated and cool them down if it's getting a little hot.
Sunshine does wonders for chameleons, so if you can take the cage outside and put it in partial sunlight for an hour or two a day, he'll be healthier for it.