Bok- The amount of time required is related to, amongst other things, the size and style of kiln. I know several potters in the US and elsewhere that fire for a lot longer than 3 days (9 days is not unusual). Even similar kilns may fire fairly differently, as they seem to have personalities.
My kiln is relatively small- I fire for a total of 40 hours. I developed a system of firing over 3 days, slowing down the process, which leads to better results in my kiln and allows me to do the whole firing myself. The majority of wood kilns are fired around the clock. I have fired it flat out for 24- 30 hours with people working in shifts, but results were not as good for this particular kiln.
The first day I fire for 10-12 hours, up to 100C to dry everything out(a bit higher at the end). The second day I get the kiln to about 450 C for 10-12 hours just to distribute ash and soak some heat into the bricks. The last day I fire 20 hours, getting the kiln to about 1250- 1300 C for several hours of that. In total, I burn 2 cords of wood- which is almost half what it would require to heat my drafty log home in a New England winter!
It is a lot of work- even for my little 45-50 cu ft kiln, it takes a couple of long days just to load the work. I have loaded it without gloves in 1 C temperatures and slush, in -10C and snow, and I have fired in 35 C (The kiln doesn't make it any cooler). I fired last week and have still not fully recovered, even though I had help from a young energetic potter that wants to learn (I get mostly stiff hands and feet, but am exhausted and achy for days). I'm not saying this to complain, just to put it in perspective- the experience that you heard of from those potters is universal.
John Baymore has a larger, multiple chamber kiln. You may see us joke a bit here about the joys of wood firing. Most customers picture peaceful throwing at the wheel, and a nice little fire in the kiln like a camp fire with friends and drinks. With all that work- I still get butterflies in my stomach getting the kiln loaded and ready. Of course, I always say that I'd lose a finger for a good story.
Here's the fire coming out of my 5 meter chimney by almost 2 meters- it's no joke, even on a small scale. https://www.youtube.com/watch?v=JmoRvurASH8