Hi NewHm and welcome to Canonrumors!
I suppose only the Canon developers could answer your questions credibly. And surely they won't.
So for me it is just guessing:
From what you describe (20 sec, max 65°C ambient, not much humidity) I would expect no problems to your gear because within < 30 seconds there is not enough time for lens and body to heat up noticeably. If you let them cool down a few minutes before the next few shots this should work.
Danger comes from heat:
- lubricants have a specified operation temperature. Too hot and they flow away. Too cold and they solidify.
- plastic can deform, you'll lose alignment of optics or even wose mechanics could jam
- electronic parts with heat losses (sensor, processor) cannot be cooled anymore and get damaged.
I would expect all this to take effect after a few minutes. But I am not sure.
Danger comes from too low humidity (relative):
- materals like lubricants, sealings and everything else flexible but also condensator, batteries or other electronical components dry out.
I would expect all this to take effect after hours. But I am not sure here, too.
Danger comes from too high humidity (relative, e.g. in bio sauna or steam bath):
- condensation on electronical circuits, schortcuits
- etc.
I would expect this to take effect after minutes or hours. But again I am not sure.
I hope, I am right and your gear will serve you flawlessly a lot of years.