Generally you can start seeing their inventories get updated after the stores open (typically 10am), and then they'll be updated throughout the day. I think it depends on the store, but I have been told that they get deliveries throughout the day rather than one big delivery overnight, so you'll see inventory pop up sporadically throughout the day. I saw this a lot when I was hunting for the Pencil last week; it would appear at a store in Austin for maybe ten minutes or so and then disappear (I assume because someone had purchased it). The Pencil I ultimately bought appeared at a store in San Antonio at around 4pm.Anyone with knowledge of Best Buy's procedures know when they tend to receive deliveries daily and when they get entered into inventory?
So, bottom line, you have to keep watch all day or you can miss it if it's something people are after.