Keep chanting it to yourself as a mantra. “7 days is the max… 7 days is the max…”
Whether you are doing up a project plan yourself or accepting a project plan from vendors, each task on the project plan should last no longer than 7 days. If any task exceeds 7 days, then it becomes difficult to track the progress and the people working on the task may also not develop a sense of urgency since the discernible milestone to them is still some time away.
Most, if not all, tasks can be broken down to a maximum 7 day duration. If you find that you are unable to do it or you are working with a project planner who says “It’s impossible” (incidentally a much too common refrain from vendors…), then TRY HARDER.