Over the last 5 years, the earliest the first house has ever been announced was March 29th and the latest the first house has ever been announced was June 10th. Last year the first house was announced on April 3rd and that was Stranger Things.
So I would have guessed end of March for first announcement; however, yesterday's announcement of the event nights was much earlier than last year (this year it was 2/5/19 while last year it was 3/29/18 and 2/23/17 the year before) so maybe the first house announcement will also be much earlier.