Man, no way this is going to run on any sort of Windows environment. Guess I won't get to sneak in CTF time at work this time around.
contents = ARGV.length > 1 ? File.read(ARGV[1]) : $stdin.read
That's just allowing you to send the test files in on the command line. From there, you can measure the time using PowerShell's Measure-Command like so:
Measure-Command {ruby .\level0 "test/data/words" "long.txt"}
Assuming ruby is in your PATH and the "test/data/words" is a renamed words dictionary file. It's a little work but you can definitely do it on Windows. I'm working on getting the python test harness to work on Windows.
It's a bit of a shame the test harness isn't Windows compatible; it's rather small, and it doesn't look like the fixes required would have been very difficult.