Is there somewhere official where the list of upcoming Congressional hearings are published?
(I am, in part, looking to find when prior ones were initially anounced)
According to the Congress.gov website (links in original):
Announcements about future hearings are available from the House Committee Repository calendar, the Senate Daily Digest Committee Meetings/Hearings Schedule, and the most recent Daily Digest in the Congressional Record.
I'm not sure if any of these provide a way to find when a hearing was actually announced, but the links from the quote are your best bet for that.