The workshop module is rather versatile and therefore it is difficult to test it exhaustively. Please let me know if you notice anything strange.
Wow, this really makes Workshop much easier to use and administer! The new "unified" view makes a lot more sense. Before, I couldn't figure out exactly when I was expected to "change phases," so the assess/submit start/end times resolves this issue for me. Your changes (after a 'cvs update -dPA' into my 1.4.2+ tree) worked flawlessly.
I've updated my course-wide date modification page to reflect the updated assess/submit/final grade release start/end times.