From his blog post announcing it (http://esr.ibiblio.org/?p=6311)

The C/UNIX library support for time and calendar programming is a nasty mess of historical contingency. I have grown tired of having to re-learn its quirks every time I’ve had to deal with it, so I’m doing something about that. Announcing Time, Clock, and Calendar Programming In C, a document which attempts to chart the historical clutter (so you can ignore it once you know why it’s there) and explain the mysteries. What I’ve released is an 0.9 beta version. My hope is that it will rapidly attract some thoroughgoing reviews so I can release a 1.0 in a week or so. More than that, I would welcome a subject matter expert as a collaborator.