Yea, there's no single answer to this. I've had mine outside for days at a time or for only 30 mins, it depends on how hot it is outside. If he has access to shade he can stay out longer, and you can mist him every little bit to keep him cooler if it's maybe around 80*+ outside. I mist quite a bit if it's over 80* usually. Watch his body language, if he looks like he's overheating or is pacing around like trying to find shade then you can bring him back inside.
Given where you live, I would be extremely careful. When you hit those hi temps with no humidity the cham will not do well outside. They do sell those swrily stand up misters you could put next to his cage, that and access to shade would help him enjoy life a lot more. I still would not leave one that size out for over a couple of hours and not in the hottest part of the day. jmo