How can you determine erratic when there is no fixed schedule.
I don't bother chasing when an auto update is done, I get the notification or an error if there was a problem. I leave it to avast and don't get concerned if there hasn't been one for many hours. Whilst in most cases I usually get one when I first boot usually around 11 - 12 UK local time, but I don't get concerned if I don't.
Don't lose sight of the fact that there are also streaming updates throughout the day (22 so far today).