A calling window is the hours during which an agent is allowed to dial. It is a small setting with two large consequences: it governs complaints, and it roughly doubles most people's estimate of how long a batch takes.
Set it on the agent, not in your head
The common failure is treating this as a scheduling discipline — "we only start batches in the morning". Then someone starts a large batch at 5 PM, it runs for six hours, and it is calling people at 11 PM.
Configure the window so the system enforces it. A batch started at midnight then simply waits and dials in the morning.
Choosing hours
Promotional calls in India are restricted to 9 AM–9 PM. But legality is the floor, not the target — a call at 8:55 PM is legal and still produces a complaint.
Sensible defaults for business calling: 10 AM to 7 PM. Avoid 1–2 PM if your audience takes a lunch break. For candidate screening, early evening consistently reaches people that late morning misses, because they are away from a desk they cannot talk at.
The arithmetic people get wrong
Wall-clock time for a batch is calls × minutes ÷ concurrency. But that assumes dialling around the clock, and you are not.
Two thousand calls at 4 minutes with concurrency 5 is about 27 hours of dialling. Inside a nine-hour window that is three working days, not one — before retries.
If the shortlist is needed Wednesday, that batch starts Monday morning. This single miscalculation causes more missed deadlines than any technical problem.
Use the window as a retry strategy
Since a second attempt should be at a different time of day anyway, let the window do the work: first pass late morning, retry pass early evening. Same list, two populations, no extra thinking.
One time zone, mostly
Everything runs on IST, which is correct for an entirely Indian list and worth remembering if any part of your list is not. A "9 AM" window is 9 AM in Delhi regardless of where the number is registered.