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?
That depends on the state. Some do require waiting periods for buying guns.
Do they require waiting times after you attached a flashlight or switched to a bigger magazine, though?
Because that is what Google is doing here - enacting limitations / hurdles for phones that were already sold.