Source: As worded by Indian Railways, Government of India

If an unused unreserved ticket is presented for cancellation, full fare is refunded after deducting the per passenger clerkage charge provided that the ticket is surrendered at the ticket issuing station.

1. Within 3 hours after the actual departure of the train for which the ticket was issued OR
2. Within 3 hours after the actual departure of the last train of the day for the destination station, for a ticket valid for whole day.