I work in publishing (on the acquisitions and editorial end) and, at the latest, we hand the edited manuscript over to production (the people that make the word document a book) between 3 and 4 months before the publication date.
Art, tables, charts, etc. are sometimes not handed off until as little as a month and a half before the book is set to hit shelves.
Additionally, there are times when production is working on formatting and stuff long before the manuscript is complete. In that case, the writers and editors have a lot more wiggle room.
Remember that having a June pub date in no way means 1 June. It's likely the books'll hit stores at the end of June.
Finally, if they're *going* to move the pub date, they'll need to do it sooner, rather than later. Their credibility isn't damaged too horribly if they do it well in advance.