好了，在wildfly datasource schemas中找到了它：

<xs:complexType name="timeoutType">
<xs:sequence>
  <xs:element name="blocking-timeout-millis" type="xs:nonNegativeInteger" minOccurs="0">
    <xs:annotation>
      <xs:documentation>
        <![CDATA[[
          The blocking-timeout-millis element indicates the maximum time in
          milliseconds to block while waiting for a connection before throwing an exception.
          Note that this blocks only while waiting for a permit for a connection, and
          will never throw an exception if creating a new connection takes an inordinately
          long time. The default is 30000 (30 seconds).
         ]]>
      </xs:documentation>
    </xs:annotation>
  </xs:element>
...