I second mas985. My controller stays on all summer. After it rains or we have a few cold nights, it will kick on, even in July & August.

Extending the season isn't anything to sneeze at, though. We opened about 3 weeks ago, the water in now 85+. We will swim until almost the end of October in 80+ water. No one else, and I mean no one, will do that around us (unless they get solar!!)