The annoucement emails take a really really long time to go out. It's dependent on each individual's contect preferences whether they receive them via email, and there are many accounts with multiple contact points. The announcement I sent on Friday was sent to something like 75,000 people, which can take awhile.
That said, it can definitely be made faster than it is now!
And as often happens, we weren't expecting to do the maintenance that took place on Friday, but the Panel and backend jobs were getting so borked up that we felt it was important to do it pretty much ASAP.