The film takes place in 2012. At the beginning of the film, Heather Miller is shown to have been a baby in 1973. This would make Heather at least 39 years old. However her character is obviously much younger than that (her actress Alexandra Daddario was only 26 years old at the time of filming).
During all scenes of the VW camper van driving around on the grounds of the house there is tyre squeal this would indicate rubber on tarmac/concrete although all the drive consists of is dry dirt track which would make no noise at all.
The date that the farmhouse was burned and the family was killed was August 19th. However, as seen later in the film when Heather is looking at the newspaper, the story was on the front page of the paper dated August 19th. The event would have occurred after the newspaper was printed and distributed.
When Kenny is dragged into the basement he drags the carpet on the stairs down with him. After Heather escapes from the basement a few minutes later the carpet is back on the stairs when she runs up them
When a character uses FaceTime to show other characters what he sees in the Sawyer house, his iPhone clearly focuses (indicated by the blue square in the center of the screen) which does not happen during a video call, indicating that he was only on his camera, and switched to it every time he was re shown.