Build starts with
$ cvs -Q -z3 -d :pserver.... co -P -d workspace -D "Thursday, February 17, 2011 2:05:41 PM UTC" om

tagging build result with:
cvs -d :pserver.... rtag -D "2011-02-17 15:05" om-build-2537 om

The -D option has different timestamps, so the checkouted can differ from what will be taged.