Custom modules and add their own dates to the list the Date API Views filter and Date API Views argument can handle. See the following example for the way that core dates have been added:

/**
 * Implementation of hook_date_views_fields().
 * on behalf of core fields.
 * 
 * All modules that create custom fields that use the 
 * 'views_handler_field_date' handler can provide
 * additional information here about the type of
 * date they create so the date can be used by
 * the Date API views date argument and date filter.
 */
function date_views_date_views_fields($field) {
  $values = array(
    // The type of date: DATE_UNIX, DATE_ISO, DATE_DATETIME.
    'sql_type' => DATE_UNIX, 
    // Timezone handling options: 'none', 'site', 'date', 'utc'.
    'tz_handling' => 'site',
    // Needed only for dates that use 'date' tz_handling.
    'timezone_field' => '', 
    // Needed only for dates that use 'date' tz_handling.
    'offset_field' => '', 
    // Array of "table.field" values for related fields that should be 
    // loaded automatically in the Views SQL.
    'related_fields' => array(),
    // Granularity of this date field's db data. 
    'granularity' => array('year', 'month', 'day', 'hour', 'minute', 'second'),
  );

  switch ($field) {
    case 'users.created':
    case 'users.access':
    case 'users.login':
    case 'node.created':
    case 'node.changed':
    case 'node_revisions.timestamp':
    case 'files.timestamp':
    case 'node_counter.timestamp':
    case 'accesslog.timestamp':
    case 'comments.timestamp':
    case 'node_comment_statistics.last_comment_timestamp':  
      return $values;
  }
}