Tim,
When I was younger and motel rooms all had adult movies I could time my "event" so that as the light on the box on the TV would start to blink - meaning that I was about to be charged because the preview period was coming to an end- I would "finish".
I got so good at this that pretty soon any kind of flashing light was enough to insure a good time.
The problems started when I couldn't figure out how to program my VCR and it kept flashing "12:00".