At this web page: http://community.rti.com/rti-doc/45f/ndds.4.5f/doc/html/api_java/interfacecom_1_1rti_1_1dds_1_1publication_1_1DataWriter.html#908102c9730fb19be447ed4af01da75e
I found documentation for the write_w_timestamp_untyped. The documenation says, "Publish a data sample using the given time instead of the current time".