Once you do your initial stability tests with your system running at stock frequencies, you can ramp things up and overclock right away. There's no break-in/burn-in time required.
I say that you should do your initial stability tests first because if your system isn't stable at stock frequencies, there's a very good chance it won't be anywhere close when you start changing settings.
Years ago, a very popular thermal interface material (TIM) called Arctic Silver used to have a burn-in time of a few days, but if you have a strong enough cooler (which the H80i/H100i certainly are)
), it's no longer an issue as the capability of the cooler itself will carry you past any of that.
I'm not even sure any of the TIMs that I use now even have a burn in time, and if they do, it's not suggested anywhere in the documentation.