A crew's specific shift plan template and subscription to common templates are either effective for a specified number of weeks starting from their effective date, or they may be perpetual, which means they have an effective date but no end date.

The crew can switch from a specific shift plan template designed just for this crew or subscribe to a common template, and vice versa over time, but their shifts may be generated by a single shift template at any given point in time. In other words, a crew's shift templates must never overlap in time.