10 minutes to a couple of hours a day will eat most higher output lights. My CR123 lights have burn times on max at like 1-2 hours, period. If you dial them down to moonlight, all models of modern flashlights (of high quality) can be dimmed down to lower burns that will last sometimes days of continuous use.
When I'm deer hunting, for example, I can set my FourSevens Quark Pro in AA (with a max burn of 205 lumens, mine is 180--older model) on moonlight mode (which has a burn time of 720 hours), walk way to mark the spot of my pack or truck, track and gut a deer, and walk back with no fear of burning out the light.
The LD22 (I guess they no longer make the LD20, the one I had) has a max run time of 150 hours on two AA's. If you are using the highest setting, it only has a run time of 2.5 hours (at best).
The Surefire Ultra is comparable to the LD22:
http://www.surefire.com/charts/flash.../u2-ultra.html
Run time of 2 hours at 140 lumens at high, and run time of 175 hours on low at 2 lumens with CR123 Batteries. 'Cept it costs $299 for some reason.