Mike didn't intend to be as gone as long as he did, so he didn't really mention the fact that he was taking a time travelling vacation. Besides, if he was gone long, he thought he could just come back to the moment that he left.
Apparently time travel didn't work like that. Returning back, according to Skeets, could severely rupture the timeline and cause mass chaos. Of course, Booster felt that way right now about Jesse coming over.
He sighed before opening the door and greeted her with a "Hi???"