latex paint takes time to cure. heat and humidity will make it a longer process. ever notice that when you paint a wall with latex paint, it will be easy to ding for awhile, then will harden? i use latex paint too. i just buy the oops paint for 5 dollars a gallon, or the paint from the city recycler. in the winter, i dry them in the house. in the summer, in the sun. if they stick or ding, i'll just touch them up next year if they need it.....