If you want to buy the Apple Watch model of your choice at an Apple Store at launch, you should consider pre-ordering online or through an Apple Store reservation, sources have told 9to5Mac. Due in part to the number of different models, Apple Watch inventory at many Apple Stores in the United States will be heavily constrained at launch, with priority given to reservations, meaning that Apple Watch availability for random walk-in purchases on day one will be noticeably tight.

As one source at a flagship Apple Store said, “we’re told to treat launch day as if there will be no walk-in stock.” That doesn’t necessarily mean there will be absolutely zero Apple Watch units to buy at launch if you don’t have a reservation, just that the specific Apple Watch variant a person wants will be far harder to come by at launch than some previous iPhone models.

Of course, inventory will vary depending on the store’s location, including state and country, with China expected to have larger stock allocations. But several sources across the United States are reporting a similar emphasis on the majority of stock being available solely for reservations at launch. Besides the U.S. and China, the Watch will be available in Canada, France, Japan, Germany, and the U.K. at launch.

Apple’s inventory plans could change, of course, if the company can pump out enough Apple Watch units before launch to satisfy all initial demand.

Beginning on April 10th, customers will be able to visit an Apple Retail Store, try-on various Apple Watch collections, and reserve a unit to be purchased and picked up beginning on April 24th. As we first reported, try-on sessions for the Apple Watch Sport and stainless steel Apple Watch will be allocated for 15 minute periods. Try-on appointment booking will begin on April 10th, but appointments are not necessarily required.

Sources now say that Apple Watch Edition appointments could last up to 30 minutes as earlier reported, but one source also said, “it’s not like we’ll kick out the Sport and stainless steel customers if they’re taking too long.” As expected, the 18-karat gold Apple Watch will be limited to Apple’s highest traffic flagship stores.

We earlier reported on a fashion and iPhone upgrade emphasis for these try-on sessions. Customers will be able to also place pre-orders online starting April 10th with home deliveries beginning on launch day, April 24th. Unlike with past iPhone and iPad launches, the Personal Pickup service that allows a person to order a device online and pick up at the store will be unavailable, but this may change in the future as inventory becomes more widely available.