I pre-ordered the 42mm SS Milanese at 8:01am, confirmation email by 8:02am. I ordered via the iPhone app as the main site didn't go live until 8:09am, that happened with the iPhone 6 pre-order as well.
Mine was shipped at around 10am this morning via UK Mail, so hopefully it should be with me Friday
Never had UK Mail deliver any Apple items to me before, it's always been UPS. UPS delivered my 3GS, 4, 4S, 5, 5S, 6+, iPad 1, 2, 3, 4, rMini and Air 2 all without issues.
UK Mail I very rarely get, though they do tend to deliver early in the day, UPS 90% of the time deliver after 3PM.
All couriers around here are very good though, never had an issue with any of them luckily.