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!!!

You use butane bottles to refill your canisters?

I'm not really impressed with butane performance in the cold to say the least...

I'm not actually sure that refilling is cheaper and i don't think it's recommended either. I found canisters at the BBQ section which are butan/proane mixes which where per gram almost as inexpensive as puncture style canisters or butane canisters.

(BBQ and DIY stores sometimes seems to have inexpensive butane/propane lindell valve canisters)

Not the best choice for really low temperatures for sure. But I doubt that's a serious issue for most people, at least as long as we're not talking polar expeditions or hardcore climbing. A liquid fuel stove would be better for that kind of stuff but it's fairly expensive and not nearly as user-friendly.

I actually already have issues at around 10 degrees celsius. I have stoves with full butane canisters, cranked full open and only had a flame which look more or less like a candle.

I refill from the Asian butane bottles just as part of my hobby and not to save money or try to get better results.
in the winter when it gets sub zero here in Minneapolis I put the empty's outside and the bottles in hot tap water.
In a few minutes the refill is done.on some old carts the Lindal valve has been used so much it won't work.
this Fall I had a cold morning and the stove was a hard light so I put it under my jacket and that was enough to warm up the butane and after it lit the heat off the burner kept it roaring.
if I went off in really cold winter weather I would take my old multi fuel Optimus 111. stocking up for an emergency I would buy all the best brand new.

how about this example of Gaz at low temps!
on a cold evening I could not get the water to boil.
I ended up spooning warm water out of the pan and onto the baseplate.that was enough to heat the cart to the point where I got a good flame that kept the Gaz running.

A great idea, but I'm not comfortable with an open flame in the tent.

no real open flame with the lamp/heater. a small Gaz lamp mantle inside that metal cage is putting out the heat.
any problem would be the hot cage touching nylon and melting a hole thru it.

Can you use a Coleman 1lb cylinder in place of the Gaz canister?

Different thread pattern on the cannisters, I think. Also designed for a different fuel mix, so straight propane would probably burn too hot and damage the unit.

Mr. Heater makes a catalytic heater that mounts on a 1-lb. propane cylinder, which would be a better choice for people using that fuel source.