After reading https://support.atlassian.com/organization-administration/docs/keep-track-of-maintenance-windows/ I understand that alerts about maintenance downtime are usually not sent, unless Atlassian deviate from the schedule.

In our organisation we work across three different time zones, and the maintenance window is set to California PST. Maintenance hits our European and Indian teams as a surprise in their most productive hours.

Thus we absolutely need such alerts, not matter whether they are on schedule or off schedule, and we need them in time to plan our work accordingly. This should be possible!