There are alot of factors here.
1. Age of the insect. Screworm Flies and most Blow Flies in Oz will live two weeks. Life cycle aswell (basically flies eat then f $%^&).
2. Altitude of operation. Some flies are ok at high altitudes, where they normally prevail.
3. Temperature. Effects flies activity and energy burn.
4. Sunlight or darkness. Direct warmth.
5. Species of Fly. Relates to the robustness of the species
I have dropped Sterile flies on different occasions for around 4 years on an off. Screworm flies over the Jungles of Central , South America and the Carribean, and Mediterrainian Fruit Flies over Southern Mexico. Altidues varying from 1000 ft agl to 14,000ft.
But I will ask the a Doctor Entamologist, colleague of mine tommorrow to give you a definitive answer.
Regards
Sheep