A new strat/trick helped me get this WR. Just watch the vid and you'll notice "OBJECTIVE A COMPLETE" appear with 1 second left in the run.
Basically, its all in the mine before Xenia. Simply do not detonate this mine, and switch to the AR33 right away. This will help because you can start shooting earlier, as well as being less lag making it much easier to kill Xenia.
Just don't forget to detonate that mine later on in the run. As you see, I found it easiest to detonate it on that final stretch before the lift door.
Anways, 23 WRs ties me with Wouter in total WRs, but I'm ranked lower since he has more untied. This WR took me under 10 hours, so its not that hard. I'd say maybe 8 hours or so.