I just spoke to an Apple Store representative over the phone who informed me, with confidence, that earliest orders are still expected to deliver by 4/24 (if your timeframe is 4/24–5/8, of course). He went on to explain that such orders are expected to ship on 4/23, so that it will more than likely be the case that no one will see a "Preparing for Shipment" change in their order status until the 23rd. I know that Apple Store representatives have the reputation of not always providing accurate information, but in my personal opinion, this particular representative seemed to be well aware of this new pre-order process and what customers should expect.
P.S.: Subscribe to UPS My Choice if you haven't done so already. Orders may ship via FedEx, depending on your locality, as is the case for nearly all Apple orders, but it is still worth the effort. UPS My Choice (if you download the UPS app) will send you a push notification, quite literally, the second your package's tracking number is entered into the UPS system, almost always before the shipper updates your order information; it's quite convenient and I rely on it heavily for all packages I know will be shipped via UPS. A word of caution though: In registering, you'll have to provide your address, and only residential addresses can be verified and used; so for those of you who posted your order will be shipped to your college campus or place of employment, you will, unfortunately, not be able to use the My Choice feature.
Best of luck.
