The series mines material from the 19 years that follow Episode III: Revenge of the Sith and precede the Episode IV: A New Hope. In other words, using the life of the Skywalker twins as a measure, the series is active in the story years that come after their separation as newborns and before their (unwitting) reunion on the prison level of the Death Star.
This show started out as Grim & Evil which combined The Grim Adventures of Billy and Mandy and Evil Con Carne In The Grim Adventures of Billy and Mandy, we meet the idiot named Billy and the snotty girl named Mandy, who apparently win a bet with the Grim Reaper over a sick hamster, making him have to be their best friend forever!