Admin -> Alert Schedules manages named, reusable time windows (e.g. "Business Hours") that an alert rule can be restricted to. A rule with no schedule attached is always active, same as before schedules existed.

Each schedule holds any number of windows (Day: Weekday/Weekend/Daily, plus a Start/End time). A schedule with no windows never fires for anything attached to it. Each schedule shows Active now / Not active now so you can check your configuration is actually right without waiting for a real job to complete inside (or outside) the window. Both the schedule name and any window can be edited in place, and Duplicate copies a schedule's name and every window as a starting point for a similar one.

Two things worth knowing:

• No overnight wrap. A window can't span midnight -- enter "after hours" as two windows instead (e.g. 17:00-23:59 and 00:00-08:00), one for each side of midnight.
• Server-local clock. The window check runs against the local time of whichever Worker actually ran the job and is now routing its alert -- not a fleet-wide timezone setting.

This is how you route the same job/outcome differently by time of day -- e.g. a Business Hours rule notifying the day team via one Style/Channel, and a separate After Hours rule notifying on-call via another. Each rule is independent, and a gap where no rule's schedule matches is fine and often intentional -- nothing fires during that time.

See also: Setting Up an Alert Rule.