I can't find it, how does the scoring work in this game?

Title.

I tried searching for about twenty minutes but no luck.

It's really hard to do isolated tests.

The scoring does seem really weird if you don't know how it works, and the game does not clearly explain it anywhere, but it's just a very simple calculation.

The game runs at 60 frames per second, and your score is the number of frames left until you die. So,

score = time x 60

Thank you very much! I was wondering what the default number was.

Is that even true? I recall playing a level where you start at the door (basically, instantly done) and getting 5999 points - but, you get 90 seconds at the start, right? Does the game run at 66.667 frames per seconds?

It's true, if you start at the door - and there is no collected gold - you get 5399 points (which is 90 seconds minus 1 frame).

Here is one such level:
www.thewayoftheninja.org/nv2.html?l=137673