Telling how long propane will last given vague conditions is hard to answer. I will tell you that on a trip to Arizona in October of 2019 that we burned through almost 20 gallons of propane in 7 days, though use was variable with night time lows ranging from the low 40's down to 12F from before sunset until about 10am the next morning one night. Given how much the furnace ran, I suspect that one 12F night with wind blowing accounted for a large fraction of the propane used. This also included propane for cooking, running the absorption refrigerator, and the propane water heater with 5 of those 7 nights being off grid camping.
p.s. may have been 8 days from propane fill up to fill up