This takes place during before "Not what he seems" Mabel and Dipper found one of Blendin's Time Machine. Both wanting to go to different Time periods they fight over it. They accidentally go 30 year back, But when they appear neither of them see one and other. Around Dipper is the familiar seen of Gravity Falls. Meanwhile Mabel arrives outside a barren apartment building states away from Dipper. Be warned this is probably ganna be Dipper centered...cause he's great...and a lot of Timestuck focuses on Mable and Stan.