[curt.clifton]

This isn't exactly a calendar-based approach, but I think it goes well with your idea. Have you thought about putting projects on hold on a weekly basis? You could look at your calendar for the week, estimate what "on task" time you'll probably have, pick the projects you'd like to work on, then put all the others on hold. Now when you're ready to get some things done you'll have a very concise list of actions to choose from in the moment.