The attached patch adds a "-t" argument to "last" (and thus, to "lastb" as
well) for specifying a timestamp limiting which records in wtmp will be
examined.  In other words, "-t" says that you want to see what the state of
the system was as of the specified time, rather than as of now.  This is
very useful, e.g., to determine who was logged in at a given time.

I've submitted this patch to the maintainer of sysvinit, but I thought I'd
also submit it to y'all in case you think it's useful enough to include in
Red Hat before he does (or even if he doesn't).