Window collision
Two windows overlapping in time on systems that depend on each other. Each was properly approved, and neither approver knew about the other.
Also calledoverlapping maintenance windows · conflicting windows
Two maintenance windows overlapping in time across systems with a dependency between them. The dangerous case is not two windows on one host — that gets caught — but a window on the database and a window on the application that reads from it, on the same night, from two different teams.
What makes this hard is that each window is individually correct. Both were approved, both have owners, both are within cadence. The defect exists only in the combination.
When the check is worth anything
At the moment the date is chosen, before the invitation goes out. A warning that arrives after the window has been published to thirty contacts is not a warning; it is a report.