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Note that the screenshots shown here have been generated after changing the On Non-Working days Days behavior for both the 15:00 and 21:00 Periods. It could be readily conceived that there would be a use case for one Period in a Working Day that would be suppressed on Non-Working Days and another Period where execution took place, regardless of the whether or not a day was Non-Working. In this case the day will be marked in the Daily Plan as an execution day and there will be no indication that not all Periods will be executed on that day.
Comparison with Behavior defined using a Single Calendar
The behavior described in this article around irregularly occurring non-working days such as holidays - where execution is moved forward or postponed - is only possible when separate Working and Non-Working day Calendars are used. With the slightly simpler approach described in the Calendar Use Cases - Managing Working Day Calendars article, in which a single Calendar is used, execution on non-working days can only be suppressed.