LoadRunner Unix Time Stamp with milliseconds

I have been working with the SAP WEB protocol this week and needed to generate the windowid which is unix time (time since the 1st January 1970) but including milliseconds. Found this loadrunner function that provides unix time including milliseconds.

web_save_timestamp_param("tstamp", LAST);

lr_output_message("The time is %s", lr_eval_string("{tstamp}"));