Design a rule - help with toggling after activation

[jshimota]

I have an outlet I use for turning on a dumb device. When it gets turned on, I have it auto turn off after 120 mins. works fine, generic rule.

What I want to do is modify this so that the result is an on/off every 15 mins during that 2hr period.
So... device gets commanded to go on, 15 mins later it goes off, waits 15, goes on, etc... until the 2hr period and then stops.
At first I thought it was a no-brainer. but the problem happened if I started the device cycling, then manually interrupted it (ala - commanded it to go off). 15 mins later it came back on - as if I didn't interrupt it at all. Can someone create a simple Rule example I can copy?

[bravenel]

Are you saying that you want it to cycle unless you interrupt, in which case to stop cycling?

Since this is an outlet, all commands to it are going to be digital. So the problem is going to be how to determine which is a cycling on/off versus which is an interruption on/off. How does the interruption happen?