They do a poor job addressing the time/day. I'm never 100% sure either.
It's based on california/pacific time but they've screwed up a few times.
I can't speak to the times they've messed it up, but this patch couldn't possibly be more clear. A date/time given with a timezone is precisely when it says it is. The only possible confusion is on the part of the person failing to translate that date/time into the date/time where they live, which is a mistake on the user's part, not the company. They could publish the release time in 24 different timezones, but they probably assume that the people interpreting this are adults with access to the internet so even if they can't do the math in their heads, they can use a calculator to do it for them. Everyone in the US knows what EDT, CDT, MDT, and PDT are relative to the place they live, so it's extremely easy to convert. The EU website lists it in GMT and BST, presumably times that people in Europe are quite comfortable translating from.