I think it honestly depends on what Apple's true feeling is about their launch day window sales. They may be processing and shipping overnight for tomorrow if they feel like they are trying to get as many launch day watches out to customers. Otherwise, if they just send them next day without a Saturday delivery, then it probably won't be until Monday/Tuesday.
I'm one of the "preparing to ship" folks that got added earlier today. Hoping to hear something about it going to ship around 5pm or later.