The <and> tag selects files that are selected by all of the elements it contains. It returns as soon as it finds a selector that does not select the file, so it is not guaranteed to check every selector.

<fileset dir="${src}" includes="**/*.php">
  <and>
    <size value="1000" when="more"/>
    <date datetime="01/01/2011 12:00 AM" when="before"/>
  </and>
</fileset>