I treat my new packages 6 days after the queen is released. After I make sure the queen is laying. Based on the brood cycle. Eggs hatch on day 3 1/2 but the worker develops more slowly. From day 3 1/2 until it is capped it is called "open brood". It is not capped until the 9th day (for large cells) or the 8th day (for natural sized cells.