The opening sentence establishes a specific time frame for the events that follow, providing context for the story. It sets the stage for the events that will unfold later. The sentence suggests a chronological order in which the story will be presented.

Could you say this exactly how it is, 3 sentences but simpler?

The opening sentence tells us when something happened and gives background information. It helps us understand what will happen in the story. It also hints that the events will be told in the order they happened.

The first sentence tells us when things happened in the story. It helps us understand what will happen next. It organizes the story in a clear order.

The first sentence says when things happened, so we know when the story takes place. It helps us understand what will happen next. It also tells us that the story will be told in the order of how things happened.