The Ops manual I believe has a 30min daylight cut off included 'to allow for visual manouevering in the event of an engine failure'. In this case the visual manouevering option was not needed as the flight was light enough to meet SID climb requirements OEI. The flight passed the SID set HDG point well before ECT.
This 30min cut off rule was originally written to cover turbo prop scenarios which lack OEI performance to climb out of the Queenstown Basin.