It is actually kind of common in Germany that landlords attach copies of news articles about the need for correct ventilation or similar "notes" to rental contracts when handing them over to a new resident. Not exactly part of the rental contract (because it's not legally possible to dictate the exact ventilation cycle desires of the landlord in a rental contract), but still a very clear hint at what's expected of you.

I've never assumed anyone to actually do all of this excess ventilation, though...I've always been too lazy to "open all windows three times a day for five minutes each" (where the heck do people find the time to do that each and every day?), and the "solution" of just opening the window a little over a long period is so obviously expensive in terms of heating costs that I rather keep most windows closed most of the time (except bathroom after showers for obvious reasons).