Seriously guys, you need to read the description on the page.
If it isn't working for you, debug your game and set the values as low as possible (3 to 15 for instance) and try it yourself.

The logic behind is this:
Kill the maximum threshold (e.g. with my values on my current run, 150 zeds minimum (1%-ish) to "start" becoming desensitized up to 1000 (100% chance) to becoming totally desensitized) and go to sleep during nighttime.
The lower your threshold is (e.g. killed 300 zeds so far) the lower is your chance getting the trait/perk.

The trait/perk once will be added by your threshold ONLY by going through from one day to another, which means, the clock needs actually to hit 0:00 AM. This is where the script triggers.
You could also adjust the script to work every 1/4 daytime (e.g. 6am, 12am, 6pm, 12pm), but anyway.
It does work.