I live somewhere that gets very hot, and they do occasionally stop flights from taking off due to the heat (usually when it is around 47 - 48 degrees) and it is for a good reason. The tarmac can get so hot it can make the tires burst, and cause mechanical issues.
The hottest time of the day here is always between 5pm and 7pm.
I'd rather my DP be a little late than hurt in an incident...
But yes, it does suck for you