Comment 17 for bug 1836475

Attaching a debdiff for the focal version which implements a random delay of up to 1 hour. The delay is executed in the background to ensure that other cronjobs are not held up. Hopefully 1 hour is sufficient: it's considerably shorter than the 24 hours that the systemd timer "smears" this action over, but mitigates the issue of an update being missed because the server is shutdown / rebooted during the delay.

Test build available in the following PPA:

https://launchpad.net/~waveform/+archive/ubuntu/update-notifier