Google details new 24-hour process to sideload unverified Android apps (Ars Technica)

Ars Technica describes
the ritual that will be required before a future Android device will
deign to install apps from somewhere other than the Play Store. It is not
for the impatient.

Here are the steps:

• Enable developer options by tapping the software build number in About
  Phone seven times
• In Settings > System, open Developer Options and scroll down to
  “Allow Unverified Packages.”
• Flip the toggle and tap to confirm you are not being coerced
• Enter device unlock code
• Restart your device
• Wait 24 hours
• Return to the unverified packages menu at the end of the security delay
• Scroll past additional warnings and select either “Allow temporarily”
  (seven days) or “Allow indefinitely.”
• Check the box confirming you understand the risks.
• You can now install unverified packages on the device by tapping the
  “Install anyway” option in the package manager.