Comment 3 for bug 1824088

This IS related to daylight saving.

The script: /usr/lib/apt/apt.systemd.daily check that the script is not run twice at the same period.

The script checks the date of today and the date of the last timestamp to determine the the diff.
The interval is calculated using the number of seconds per day multiplied by number of days.

If a day in the interval has less then 24h this check fails.

This also affects the apt-daily.service that updates.

This is not only Xenial but all the way up to 20.04/Focal.