I dug deeper into the subject, to prevent excessive load on mirrors due to clients downloading updates and metadata at the same time.
Upstream defaults for anacron and yum-cron:
- Anacron job hours 3-22
- cron.daily job starts at minute 5
- Anacron random delay 45 m
- yum-cron random delay 6 h
In other words, a CentOS server that is not switched off overnight starts yum-cron from 3.05 AM up to 9.50 AM, local time.
The 6 hrs random delay locks the cron.daily job for a long time, and I don't like this aspect. I can see the evidence of it in my log files.
However, NethServer Enterprise runs the CentOS default value. It proved to work well against Nethesis mirrors. For this reason I'd apply the same 6 hrs delay to the Community edition, too.