Deltarune: No, hacking your HP does not effect the Dog Jumpscare 

("Then why did I post this video" -me) So that trying it is archived and can be known that it doesn't work. Answers the question anyway also did you see the end I left in? I got the Tree Room on the first try, that was complete luck.
I also did this with 999999 to truly confirm but no difference in murder time.