Fix Phame Post creation time

Summary: I spent way to long to arrive at this solution. Ref T9360

Test Plan: Publish a new post, see time, unpublish post, see draft. Start a new post, wait 10 minutes, publish, see "now".

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T9360

Differential Revision: https://secure.phabricator.com/D14656