Jeff..hours! I have never kept track just how long they last.
i'm kind of a Gaz hog and on a 12/13 night canoe trip i'll use four full 8oz cans and maybe 1/2 of a fifth that was used on 4 meals.the last breakfast just being coffee and oatmeal.
the other meals are sort of Gaz heavy making pancakes,bannock,
a big egg and rice breakfast.dinners are rice packs with freeze dry meat that call for some simmering.
the night I got wet and ran the burner in the tent for several hours. full blast for 15 minutes and then low for a couple more.there was enough Gaz left for breakfast and dinner.
I don't try and squeeze every bit out of a can and i'm sort of sloppy like letting it burn for 10-15 seconds at the start when I adjust the flame without a pot over it.
a couple buddy's made a light weight trip into Canada and using one of those Orange Box stoves went for 10 days on one cart and a bit of a second.they had cold breakfast and lunch's and just boiled water for freeze dry meal bags.
I would say I get three full days out of a cart which I refill at home from the Asian butane bottles.
I always have a back-up cart in the bottom of my gear bag but have never used it.
I moved from Coleman fuel a few years ago and was using just over two quarts with a pint back up that did get used a few times.
if I was hiking rather than canoe tripping which goes out heavy,two 35/40 pound Duluth packs, I would be a lot more careful on fuel use!!!