I figure it's referring to fifteen hours left in today, and then all of Monday. I think on Pacific Standard Time (my time zone), but then again it could base the time on where my ISP indicates I am.

Speaking from an industry standpoint, pre-orders can't even get theirs early if the book's classified as a Strict On-Sale. SOS books are under an embargo, and if released early, the store that sells them gets in deep trouble. Like, huge fines trouble. Some stores do it anyways for some reason, but as to why they'd want to risk it? Search me.