The Steemit dev team has submitted a pull request to update the date for HF 17 to Tuesday, 21 March 2017 at 15:00:00 UTC (11:00:00 EDT).
Disclaimer: I do not work for Steemit. This is not an official Steemit post. Everything in this post is subject to change. I am just reporting what I see in the Steem GitHub repository.
[Edit] Just adding that it is possible/likely for this date to get pushed back again.