If they truly turn over in just a day then that's fine, but in general you are correct that you don't want them in very hot temperature for too long.

I got that same coupon twice this year so far and it's a great deal. The Hasa 12.5% chlorinating liquid I get is normally $3.85 per gallons so with 25% off it's only $2.89 per gallon. I like the fact that I get a 4 gallon crate at a time and I return the bottles for reuse -- much better than recycling or trash.