Currently, viewing or changing the maintenance window of a site is restricted to Atlassian Support, as documented in: Keep track of maintenance windows

View or change your maintenance window

Your maintenance window is chosen based on the timezone when you sign up.

To view or change your timezone, create a support ticket and let us know your preferred timezone. Contact our support team

As a Site or Org admin, I'd like the ability to view or change the maintenance window of my sites.

WORKAROUND to check the maintenance window :- 

1. Attempt to set the Data residency for the product (Note :- Do not complete all the steps :- we just need to validate the window in step 2 "Select move window" and cancel the process)
2. Select Set location
3. On Select a move window page user will see option (if downtime is less than 2 hours) > Schedule move in the maintenance window
4. This option will show the current 2 hours maintenance window set for the site as shown in the below screenshot :-