What's the delay from announcement to store update?

It can vary between few weeks and few month. I am afraid its not something one can reliably predict. The question whether they will 'announce' new products at WWDC or whether they will actually release them. In the later case, it is usually possible to order the items instantly from the online store (will take a week or two to arrive). The physical stores should get the new models within 1-3 weeks, but some of them (mainly the prominent ones) will already have them on the next day.

 

You can also return it for store credit

 

I would consider it unlikely that there will be new Macs at the WWDC. If there would be the roll out is quite quick usually with actual apple stores but most in Europe are only resellers. More likely though a update of the mac line is still months down the road.
A couple days after NDA fall by Intel is very unlikely with all the stuff about the USB bug and tight supply early on. Macs are fairly high volume and the last few times around they updated about 2 months after a new chip release.

People are too optimistic.