To start off, I am not sure if this "tdate" is an HP proprietary thing or what. But, when I did some research on what a tdate is I came across the following site - http://www.math.nyu.edu/~neylon/tdate.php
The tdate is the day-of-year dot the-year, with the day of year expressed in base 7. By day-of-year, I mean how many days it has been since the previous year. For example, today is 420.2016.
But that doesn't match what I have (well, at least it doesn't seem to match to me).
I also found mention that it is something to do with the Delphi language, which also didn't help.
Outside of that, I am at a loss of where to start on converting the HP "TDate" to todays date and time, and was hoping that someone might recognize the below and give me a starting point. They have a tool, but that requires manual input (and that is what I am told to use when I ask how the conversion is done).
Tool example(tdate converter from HP)
time_t = 1469721083 (this is what is stored on the system).
time_t (in hexadecimal) = 579A29FB
Date / Time = 7/28/2016 11:51:23 AM (in DST)