The dates are still estimated without a firm commitment. Apple provide a link with your order which takes you to the following bookmark on their store help page.
what you said is correct it is an indication. But read the Email that was sent by Apple, it clearly says:
"Your Apple Watch will be delivered between April 24th and May 8th".
That is not saying estimated that clearly states that it will be. That is an order update and supersedes the original contract document. it is sent out to you clearly showing the Order Number and applies to your apple watch.
The original could be argued as you said but the e-mail clearly states "will be" not estimated.