I disagree somewhat with the heat/sun issue, and please, don't take this as confrontational at all...but...
If the ambient temperature is around 65F, and the sun is shining bright, the surface temperature of a painted car (especially a dark car) can easily exceed 90F. The surface of the car will get warmer as the ambient temp increases, so if it's 80F outside and sunny, expect your car's temperature to be well over 100F.
Anyway, there are solvents and carriers in most wax products that have different levels of tolerance for extreme heat. I'm not sure that I'm using the correct wording here, but some of them can "flash" too quickly and bond with the paint in a terrible way. Best case, you'll get streaking and a product that's hard to remove. Worst case, well, it ain't pretty.
I know from experience, as I've been to numerous car shows where some guy will be waxing his Black car in the direct sunlight and you'll hear him cursing as he's trying to remove the product...and these are spring car shows (temps in the low 70's).
If possible, use shade. If it's too sunny, I'd reconsider the detailing for another day- it's just not worth the risk.
Finally, when I was a tech at the Ford dealer, customer cars would sit in the sun all day long with the windows rolled up and the plastic protectors on the steering wheels/seats/floors. On the really hot days (85+), we couldn't even touch the steering wheels, because the plastic would burn us (so would the dash, etc). Just for kicks, I took my Techtronix temperature meter out with me a few times, and temperatures over 160F were not uncommon on the dash, steering wheel and paint of the cars!