Use the correct "completed" time in Harbormaster display UI
Summary: Fixes T12883. The task seems correct to me and I think this is a copy/paste mistake that probably blames to me.
Test Plan: Fiddled these numbers, viewed a build in Harbormaster, saw the adjusted time.
Reviewers: chad, amckinley
Reviewed By: chad
Maniphest Tasks: T12883
Differential Revision: https://secure.phabricator.com/D18177