From http://bugs.musicbrainz.org/ticket/5372

The timestamps in Help > View Log appear to be from when you opened the Window, rather than when the event actually happened. They're correct if the Window is open already while you're performing a task.

However one generally only opens the log window if one has had a problem, i.e. after the fact, and the timestamps of when you opened the window isn't much use for debugging at that stage, especially if you've been using Picard for a while.