It's normal behavior.
And if so by default in the future time: So Long, and Thanks for All the Fish!
(I don't like such control in an open forum)
Since we started being attacked by spammers. Moderating all new posts outside of US office hours has been the policy for months. It may change in future, but it's necessary at the moment.
I have never seen this note and there have also been posts in the out of office times.