I would only add a second rewind if it were gonna be used in some context like I said below, getting behind cover to avoid a guard then to get back out from the cover and continue on the path. Otherwise you're adding it for the sake of adding it rather than to add an extra level of gameplay.
You're not using the built in unity audio like Audiosource, Audio Mixer etc?
As for the numbers, I'm really not sure, I may be the problem as I've never been a big puzzle guy.