[Geee]

Dave said: "I saw Bob when I arrived to the kitchen at 9:30"

also

Dave said: "I saw nobody when I was leaving the bedroom at 9:15"

How could he leave the bedroom at 9:15, but arrive to the kitchen at 9:30? Where he was from 9:15 to 9:30? I assume that each transition takes 15 minutes, so that he can't step directly into the bathroom or the living room from the bedroom.