Intune-CoreImage devices differ from Classic-CoreImage devices in many ways.  One of which is how their Operating System versions receive annual updates, otherwise known as WaaS updates.  Unlike Classic-CoreImage devices, users are not prompted to install the WaaS upgrade.  Instead, the upgrade installs in the background automatically and then prompts the user to reboot.  The user may defer the reboot for up to three days after the upgrade. After the three days expire (including weekends), the system will present a 15-minute countdown before rebooting itself to complete the upgrade.  The reboot may take over 30 minutes before a user can log back in.

Once the device receives its policy from Intune to upgrade Windows, the upgrade will begin in the background. Users may not even notice it is happening.  The following screenshots from the Windows Update portion of the Settings application show the four phases of the upgrade:  Downloading, Online Upgrade, Pending Reboot, and Offline Upgrade.  The Downloading and Online Upgrade phases occur automatically and in the background.  Only when the Online Upgrade phase completes is the user notified and requested to take action.  The Offline Upgrade phase may take over 30 minutes to complete.

Downloading phase

Online Upgrade phase

Pending Reboot phase

Note that you can choose to restart now or schedule a time when rebooting the device is more convenient.

Windows will also show a notification informing you of the impending reboot in three days and give you options to restart now or at a more convenient time.

Offline installation phase
 

After the upgrade completes successfully, you will see the normal login screen and may proceed to log in.