I need to calculate how much time was spent on a bug. I saw a bug lifecycle diagram, but it's not clear when someone starts working on the bug: after UNCONFIRMED or NEW or when ASSIGNED. Any ideas?
Usually at ASSIGNED. Although somebody has to do some work in order to move it from UNCONFIRMED to NEW--usually a "triager" who may be the developer or a QA person (or may even be a separate person).
In Bugzilla 4.0 we changed the default name of the ASSIGNED status to IN_PROGRESS which is a bit clearer.
-Max