summer is a great time for box turtles to spend time outside but there is such a thing as it being too hot. the cut-off temp is 90. i will not put out my turtles if the temp reaches this. today its supposedly going to hit 92. turtles are very susceptible to the extremely hot weather. my russian tortoise katya will definitely be going outside today. these temps are not dangerous for her.
It's good that you're keeping the boxies safe inside when it gets too hot for them. It sounds like Katya is a real summer girl and enjoys the heat, though!