I don't think Valve knows exactly, because, unlike what lots of people here seem to think, it isn't as simple as pressing a button to allow us to download it. I'd much prefer late updates from Bethesda that actual tell us something, then to have them tell us they still don't know every minute.
Uhm - they *should* be prepared for a release of this type, the only thing they need to worry about is the distribution. Is it really that hard to get right?
They get all the files needed beforehand and a release date. If they can't handle that, they shouldn't agree to said release date. Now they have, and they've failed. (To the "simultaneous launch" part, set by Bethesda.)
Even if it's not as simple as to just press a button - they've still failed. Preparation? Oh, have you not heard of such a thing, Valve?