Hackernews user eastdakota (probably Matthew Prince) is the CEO and co-founder of CloudFlare (according to the HN bio) and has publicly stated that:
One of the individuals who discovered the [Heartbleed] bug contacted
us as a large provider of SSL termination services. We were asked not
to further disclose the details until it was officially patched and
announced by OpenSSL. The official announcement occurred today after
which we put up a post to let our customers know that they were
protected.
And:
...we held the post informing our customers that they were protected
from the bug until after it was officially announced by the
organizations that had discovered it as well as by OpenSSL
And also:
The bug was discovered by a researcher at Google and three engineers
at Codenomicon.
Credits:
The vulnerability was first reported to OpenSSL by Neel Mehta from
Google Security. Matti Kamunen, Antti Karjalainen and Riku Hietamäki
from Codenomicon Oy reported the vulnerability to NCSC-FI, who
reported it in turn to OpenSSL. NCSC-FI would like to thank
Codenomicon for reporting and analysing the vulnerability.
The heartbleed.com site is registered to Codenomicon
Domain Name: HEARTBLEED.COM
Registrar URL: http://www.godaddy.com
Registrant Name: Marko Laakso
Registrant Organization: Codenomicon Oy
So going from what Matthew has said, it appears that the first public disclosure was either the OpenSSL Security Advisory or heartbleed.com, and the rest is history.
The Cloudflare blog post is 21 hours old at the present time, with the Hackernews post now at 20 hours old, so the initial announcements from OpenSSL / heartbleed.com are probably not much older than that.
Edit: heartbleed.com now states:
OpenSSL Security Advisory (published 7th of April 2014, ~17:30 UTC)
Cloudflare Blog Entry (published 7th of April 2014, ~18:00 UTC)
heartbleed.com (published 7th of April 2014, ~19:00 UTC)