Peter by the wiki link it says 10 years service
Country
United Kingdom Type Military long service medal Eligibility Part-time Air Force officers, airmen and airwomen Awarded for Ten years service
https://en.wikipedia.org/wiki/Air_Efficiency_Award
As an LAC he could have been "aircrew" as gunners before they became established as a Sergeant ranked trade, and were often drawn from the engineering ranks. I remember some guy escaping Europe in a Fairey Battle having fought in France etc and being one of the lucky few Battle survivors and was amazed to find at home when they landed everyone was now Sgt aircrew and here he was a battle hardened LAC with a lot of missions behind him. Indeed he said he would fly on missions, then was expected to do his engineering trade when back at base until needed again!