It's super simple.
Extract the zip archive somewhere,
open v2.html in the browser.

D = random number from 0 to 59
F = reveal the answer
0...5 = control the first digit, e.g. 2 will limit the range from 20 to 29
6 = reset to range 0...59

2nd edit:
Too many errors in jslint, so I edited the code a bit

I think it's now a bit faster thanks to avoiding global variables

old crap below this line
changed javascript to only use keydown event, added range control
updated version

this is old version