Warmer air is less dense, so that could be a factor or with the extra ambient heat your engine was able to operate more efficiently sooner. I don't know... I'm a bio geek by trade.
But this topic renews hope that I can use my A/C some more. I live in Central California and like San Diego we're cooking like there's no tomorrow. Oh lookie, its supposed to be only 104F today! That's a relief... that cooler than yesterday.