Thanks for the quick response.
You just explained it. The randomness depended on the number of devices in the device list and the number of devices that are to be on at the same time. My device list was one and my devices on was one. I mistakenly thought there was a random Off period between on times. Now that I know how the app works I can make it work for my lighting application.
Do you know of an app that will randomly turn on and off a single device? I have a waterfall on a fountain I want to turn on for a few minutes each hour.