Thanks for the great feedback as always!
You're exactly right about the cooldown. I had wanted to prevent players from pressing all the keys at once, and so currently, if you press all 3 keys at once, only one will execute, the other two will be dropped. After getting all this feedback, I think it's clear now that that was a mistake, and I probably should have queued up those keypresses to be processed once the initial attack was finished. This is apparently what a light of fighting games do, and it makes sense in fast-paced combat, which was what I was going for here.
In regards to the very low records, the 6s record was done by a friend of mine, and I actually watched him do it. The way the timer works is that when you win, what's shown is:
time: playtime - (health * 5)
So in the case of the 6s record, it was actually (6 + (5 * 3)) so 21s. Which is still very fast! I wanted to reward players for not getting hit. But that's also not explicitly shown anywhere. I probably should have shown the math at the end like:
time: 21s
health bonus: -15s
final time: 6s