An appointed or scheduled time, especially for departures/arrivals of trains, planes, or the start time of events; often used as "on schedule".
列車は定刻に到着した。
The train arrived on schedule.
会議は定刻通りに始めますので、遅れないでください。
The meeting will start at the scheduled time, so please don't be late.
飛行機は悪天候にもかかわらず定刻に出発した。
Despite the bad weather, the plane departed on schedule.