Just because it doesn't tell you where he is doesn't mean you can't memorize people's patterns. The postoffice is closed at 15:00, and on Saturdays and Sundays. That's why he'll be gone and Wayne will be walking outside. You'll never get a part-time job notice from anyone like Ethan or Ludus whenever it's their day off. If anything the only person normally hard to find is just Kasumi.