what interval do you set between ads?

is an ad every 5 minutes too much? that's what i'm currently running, which would mean like 13 ads counting the intro and outro ad in a 1 hour video.
i don't want to scare away subs or viewers by annoying them too much, but it does grant a lot more CPM to put a bunch of extra ads in your video so i'm wondering what the right balance is.