The maintenance window nobody schedules
Every production system needs maintenance. Most teams never schedule it — until the system schedules itself, at a worse time.
Modern infrastructure marketing pretends maintenance windows are a thing of the past. They aren't. Every system needs them — for major version upgrades, schema migrations, hardware changes, security patches. The question is when, not whether.
Unscheduled is worse than scheduled
The maintenance you don't plan happens anyway, just at 3am when a long-deferred upgrade can't be deferred anymore. The team that has scheduled maintenance windows quarterly is the team that handles them as routine work, not as crises.
Schedule small ones often
Monthly fifteen-minute windows are easier to recover from than annual all-night migrations. They also keep the team practiced at the operations they'll need when something does go wrong.
Either you maintain the system, or it maintains itself — usually badly.