Are you looking for the specific utilization per flight hour (not including time used by engineers, groomers, positioning ...etc etc) or an average complete use of the APU divided up by flight hour.
I know it sounds high, but on a 22,000 hour airplane for example, our APU time is around 16,000 hours (On Condition woohoo!). This is in Chilly Canada though where we sometimes just let it run all night.