Zelda is associated with the color green. Green is associated with Ireland. Ireland is associated with St. Patrick. St. Patrick is associated with St. Patrick's Day. St. Patrick's Day is on 17th March. That’s when we'll have a Zelda Direct.
But seriously, there's a rumour that Nintendo will have announcements for the next 4 weeks.
That would fall exactly on 17th March after yesterday's Direct. It would give Nintendo an opportunity to talk about all things Zelda in more detail, 35th anniversary, Skyward Sword, Age of Calamity DLC, other possible Zelda events and products and maybe, just maybe, a new trailer for Breath of the Wild 2.