When I run git-cvsimport, the timestamps that it shows in the reflog for refs/heads/master do not reflect the actual times that the ref is updated but rather reflect commit times in CVS.
In fact, it looks as if the reflog timestamp is always set to the timestamp of the last patch appearing in the cvsps cache, regardless of what branch that patch affects and regardless of when the actual update to the local "master" ref took place.
Until yesterday, I was using git version 1.7.2.3, and as of yesterday I upgraded to git version 1.7.3.3, which is currently the highest version offered by Cygwin. Both versions exhibit this behavior.