Appropriately and not on someone else's dime.
In other words, I vary my attention to the checklist based on what's been going on with me and the airplane lately. If I just flew yesterday, I'm probably a little less detailed than if the airplane's been sitting in a damp hangar for two weeks. I also don't hog up the runway or taxiways doing checks and holding up someone else from using the facilities (same goes for full starting checklist sitting in front of the gas pumps). But I have sharper days and slower days to it's tough to say how long it takes on any particular day.