The short answer is - it takes roughly 14 days (according to most sources) of continuous exposure to warm temperatures before the body completely adapts.
For those of you reading this note there is good news. As Charlotte moves toward the middle of May and the temperatures are rising, our bodies are already in the middle of the adaption process. Therefore, by end of May our bodies should be mostly through this process.
Just remember, drink lots of water and find a shady trail for your runs.