I have been there recently in the early morning and asked specifically as I too was interested in the change in hours. I was told 0530hrs but I have read somewhere 0500hrs as well (perhaps on the M&M thread) http://www.flyertalk.com/forum/miles...unges-dtw.html

Edited - it is post #51 in the UA thread (this thread) which says 0500hrs. Post #37 in this thread reports a change in hours.

There is a midday lull before anyone comes in for the LH flights where I have been all alone in the lounge, and did ask for clarification, and was assured that it was indeed open through the day.