Persimmon trees are pretty tough, with the heat not really causing too much concern if planted with proper technique in soil that drains at least moderately well. Very poorly draining soil is about the only issue that persimmons struggle with. They do take a fair amount of cold pretty well, hardy to USDA zone 7(0-10°) and higher, so if you have at least a month or two before your first 'severe' frost, still plenty of time. If you end up having to plant in the summer to meet this time frame, plant early in the morning or late in the evening when the summer heat has lessened, be gentle when handling the root ball, and then water well.