My apologies for the double post.
All right, so I've been messing around with some ideas. The damage threshold idea put forward by jik is highly similar to what I had planned. It's easy to implement. In fact, it was nearly complete at the start of this topic.
I tried to implement something like Dance Dance Revolution where there's a certain window in which to perform an action. That's proving to be somewhat more difficult to implement, but, in truth, I didn't work with it for very long, so it may yet work. I'm not too sure that I like this one. I've never played anything like DDR so I can't really say.
I've also tried to decipher what Ash_Mantle is saying. It's not for any lack of clarity from Ash_Mantle, but, rather, a certain degree of stupidity from me. I'm currently messing with calculating the item quality based on the rate of damage a <insert time unit here>, but I don't think that's what he meant.
I think it's likely that I'll take MountainBlade's and jik's suggestions for now, since they'll be simplest to implement and move on to other things. I can come back to this.