Maintenance configurations have a separate (somewhat useless and definitely confusing) activeness window in addition to the actual maintenance periods. A simple enabled/disabled toggle would be most useful, instead of or in addition to this window, as has already been suggested in ZBXNEXT-433.
Due to the extra step of work configuring the activeness window and also to avoid anyone a little less experienced with Zabbix thinking it's the actual maintenance period, most of our configurations have the window set from 2001-01-01 to 2030-12-31. The window end date is usually in the past only if a maintenance configuration needs to be temporarily disabled. Maintenance configs are always reported as active, even if the maintenance periods have expired - this isn't a bug, but the useability could be improved a lot.
The maintenance list view could drill down into the actual maintenance periods and show the next scheduled maintenance period start and end times for all configurations.
The text "Active" could be coloured gray and state "Unscheduled" or something to that effect, if all configured maintenance periods of an active maintenance window have expired.