Is there any downtime of services during an in-place upgrade of Plesk?
How long does the upgrade take?
There is a small downtime since the services are upgraded and the new configuration is applied.
The overall downtime and upgrade time depends on multiple factors such as the spare resources of the server, number of domains, mailboxes, databases, etc., so the time that it takes to reconfigure each service and complete the server upgrade may vary from a few minutes to hours.
Generally, only the Plesk UI service will be down for the whole time of the upgrade. Other services (e.g. MySQL, Apache, Nginx) can be down intermittently until they are restarted.
Note: Automatic update is performed during the daily task which usually takes place at night.