The prologue begins with info about the time that the story takes place. There is no year listed, but the prologue makes it quite clear that the story takes place during the first week of August. That week is special because it is usually one of the hottest and stillest weeks of summer. It causes strange things to happen.
"There is no thunder, no relieving rain. These are strange and breathless days, the dog days, when people are led to do things they are sure to be sorry for after."
The three events that are narrated about all happened on the same day. One event at dawn, one event at noon, and one event at sunset.
The dawn event was Mae Tuck leaving, on her horse, for the village of Treegap. It was something that she did once every ten years.
The noon event was Winnie Foster deciding to consider running away.
The sunset event was a stranger appearing at the Foster's house. He claimed that he was looking for someone, but he wouldn't say who.