Certificates have a great timespan like "do not use before" and "do not use after". So you can't simply shown outdated certs because this make time totally use

Certificates have a great timespan like "do not use before" and "do not use after". So you can't simply shown outdated certs because this make time totally useless. But you also can't shown cert from the future. Other sad news - new browsers set that certs can have lifetime only for year and month: https://www.michalspacek.com/maximum-https-certificate-lifetime-to-be-1-year-soon https://www.michalspacek.com/maximum-https-certificate-lifet... to effective fight against certs that are too long lifetime. So this make a window for installing new cert exactly 42 days. And many people will fail on this trap soon.