Starting in August, installing APKs from unverified developers will require a new procedure called Advanced Flow. It involves enabling developer mode, rebooting the device, and waiting 24 hours with biometric verification.
After that, you choose: allow the APK installation for 7 days or indefinitely. The procedure is a one-time process and applies to all versions of Android.
Will the 24-hour wait stop you from installing APKs outside the store?
Wanna give a source for that? Everything I read said that after the 24 hour scare screen, you could optionally enable third party installation permanently. Literally nothing about certificates expiring. Where are you even getting this from?