Not long ago I talked about nAnt time stamping. It was an interesting, but unnecessary exercise. If I would have been a smart and read the whole manual I would have discovered nAnt tstamp task. It's a task to generate time stamp by template.
The new code that uses this task to time stamp projects is much shorter:
<tstamp />
<zip zipfile="${release.dir}\${project.name}.${tstamp.date}.zip">
<fileset basedir="${working-release.dir}">
<include name="**" />
</fileset>
</zip>
tstamp by default sets tstamp.date to yyyyMMdd. This is just what I needed and the code is much simpler.