[hteas]

Connor,
I don't know how anyone else does it, but I breathe out whaat little is left every 5 seconds for the first 30 seconds in an effort to make it consistent, and to speed up the reflex by emptying my lungs as much as possible without resorting to negative packing. Right or wrong, I worry that negative packing is the best way in the world to tear your lungs loose from the pleural cavity, so I keep well away from it.
The variability is beyond me. I know some days I never get past 60 seconds, and on a few I do multiple 120s. Since I can't figure me out, I have no clue about anyone else. ; )
Howard