The greatest benefit would come during winter, when shorter daylight hours restricted flights to before 5.30pm.
A ''stretched out'' flight schedule would ease pressure on airport facilities, caused by continuing rapid growth in passenger numbers, particularly a mid-afternoon ''pinch point'' caused by Australian ski tourists.
The improvements were required by New Zealand and Australian aviation authorities when they approved the airport's ''safety case'' for night flights in May last year.
Navigation technology enabling aircraft to land and take off at night is already in place.
Destination Queenstown chief executive Graham Budd had ''no doubt'' demand existed for extra flights, and expected airlines to respond accordingly.
''I think it is reasonable to assume the airport wouldn't be investing this kind of money if it didn't anticipate support from airlines.''
In the short term, he expected airlines to spread their flight schedules through the day, if not increase capacity immediately.
Queenstown Lakes Mayor Vanessa van Uden said the upgrade was a logical step in the airport's development, and would improve safety, regardless of whether evening flights went ahead.
Clutha-Southland MP Todd Barclay said evening flights were a ''game changer'' for Queenstown and the wider region.
''Expanding the airport's capabilities will facilitate more business-friendly flight hours, enabling people to travel to Auckland or Wellington for a day's business and return on the same day, a feat which is currently near impossible.''
A dissenting voice has come from the New Zealand Air Line Pilots' Association.
Its technical officer, David Reynolds, telling the Otago Daily Times yesterday it had not been consulted on the safety case for night flights, and some pilots were unhappy with safety systems and procedures at the airport.
Edghill said, apart from trenching for electrical cabling, all construction work would be carried out at night when the airport was not operating.
''All practicable measures'' would be taken to minimise the impact of the work on neighbouring residents.
Technical design is being handled by engineering firm Beca and construction firm Downer is the lead contractor.
In the year to June, nearly 1.4 million passengers passed through the airport's gates, an increase of 12 per cent on the previous year.