this is very easy to get. When Dr. Fred sends Hoagie to the past, first enter the inn, and go to the main room, it should contain 3 people, then click on the fire place and Hoagie should go up it. When on the roof, go through the open window and grab the can of red paint. Go back through the chimney and leave the inn. Go to the crono-john area and there will be a kumquat tree, use the paint on it and it will become a cherry tree and it should unlock.