Summary: Ref T2217. Fixes T3866. We need to do a little more massaging before we can set strings as the value on datetime controls. Test Plan: Set default to "1:23 AM", "2001/02/03". Reviewers: btrahan Reviewed By: btrahan CC: aran Maniphest Tasks: T2217, T3866 Differential Revision: https://secure.phabricator.com/D7116