The simple answer is to break the piece up into its Signposts (4) and Journeys (3) so that it goes Signpost-Journey-Signpost-Journey-Signpost-Journey-Signpost. That's seven segments or "acts". TV acts, like chapters in a book or acts/scenes in a play, are arbitrary units of measure imposed on the "story". The one rule you can follow is to break for commercial at a natural break in the story. This can be a break in the Objective Story throughline, the Relationship Story throughline, the Main Character throughline, or even the Influence Character throughline. With 24 transitions between signposts and journeys (12 if you look just at signposts or 8 if you look at only journeys), that gives you plenty of opportunities to find a natural break for commercials.