The ATS flight plan should be closed at the earliest possible moment after landing. The examiner wishes to emphasize that if this is not done within 5 minutes of the expected landing time, the aircraft will be considered in a Distress Phase.

ICAO Annex 2
3.3.5 Closing a flight plan

3.3.5.1 Unless otherwise prescribed by the appropriate ATS authority, a report of arrival shall be made in person, by radiotelephony or via data link at the earliest possible moment after landing, to the appropriate air traffic services unit at the arrival aerodrome, by any flight for which a flight plan has been submitted covering the entire flight or the remaining portion of a flight to the destination aerodrome.

AIP South Africa - General
GEN 3.6 SEARCH AND RESCUE
5.2.3 Distress Phase (DETRESFA)

A situation wherein there is reasonable certainty that an aircraft and its occupants are threatened by grave and imminent danger and require immediate assistance or has crashed. This phase will be declared when:

g) An aircraft which has been given approach or landing instructions at an aerodrome, fails to land within 5 minutes of the expected landing time, and communications cannot be re-established with the aircraft.