I think it will be when they go on sale - probably a day earlier as it could be done in Australia (time zone difference)?
I don't think you can tear down a 'review'/pre-release device - they probably don't give them to iFixit and they might also want them back or something afterwards?
Probably correct. I remembered the Air being torn down almost right away when it was released but that may have been a few days after release day, not just after the keynote.