How do you manage your practice time?

When I practice, it's hard to stay focused and manage how I use my time. I just have too much fun. So, I use a timer to force myself to stop. Lately, I've been planning practice sessions in advance. I break up a thirty minute session into five - five minute sessions. I know that's only twenty five minutes, but that gives me a buffer to make some notes on what I need to do next. I make a list of five, or more things in advance and keep the amount of time reasonable by limiting sessions to thirty minutes.

What works for you?