As per the public doc Keep track of maintenance windows

We use maintenance windows whenever a change, bug fix, or essential maintenance requires some downtime to roll out to your Atlassian cloud site. Maintenance windows occur daily between 1 am and 3 am in the timezone where your site's server is located.

We aim to keep total weekly downtime to less than 15 minutes, and we only use the maintenance windows when downtime can’t be avoided. Many changes require no downtime and are rolled out in accordance with your release track. Learn about release tracks

Add tickets here when customers contact Support to find out / change their maintenance window