As we all know, chins should be kept at temperatures of 72 F or below.
But what about playtime? Well, that's a bit different. Think about this for a second. Let's say you're sitting around in a room, and you're comfortable, not cold but not hot, temperature wise. Now, let's say that you decide to run around the room at full speed, bouncing off the walls. Might you get warmer, and even venture to think that you might start thinking the room is a little too warm for this? If you're not picturing this well, think of a gym. You're not likely hot when you go in, but then you start working out, and start sweating. All of a sudden, the room may not feel such a comfortable temperature anymore, even though the room temperature didn't change.
Same for the chins. In the warmer months, they shouldn't be out for playtime, at all, if the house temp is over 70 degrees. This is to prevent them from overheating and possibly getting heatstroke, which can be fatal. They can (and do!) live just fine without playtime, so for their sake, no playtime over 70!