Tim Howard answered that in the link I posted. It's 60 days from the earnings release on February 14. The March 31 date is not set in stone but it makes sense because then the draw money will be put on the books in Q1.
Also answered in Tim Howard's post. Both Fannie and Freddie will need draws because they both posted Q4 2017 losses more than big enough to wipe out the capital buffer.
I meant that the $6B combined buffer is so close to zero compared to a full recap that I don't think the stock price will react to it. Shareholders still have no access or rights to the buffer money.