Jason is being told a key piece of information that will play a central role in the story. It introduces not only Jason and Mr. Manaby, but something that will drive future events, the 5:00 policy. The act of telling Jason is not yet Rising Action, however, because it only introduces the central elements of the story. The story has not yet begun to move towards its climax.
The details create a positive mood, one of new beginnings. However, Mrs. Mallard has just received the news that her husband has died which is really an ending.
