Hentai,
I have seen a shift in release days over the past (almost) 2 years. It is not uncommon that they switch days. It used to be on monday, then switched to tuesday and now sometimes even on wednesday. If they discover a problem at the last moment, they might have to shift the release date to a later day. I would not hold on too much to a fixed release date, they varied before and they will vary more often I presume. The only fixed date (though it was missed a handful of times) is the friday.