The length of burn time has a lot of variables.. the heat the house is asking for, the depth of the fire, the strenght of the chimney draft etc.. If you have a deep load of coal,, say it is up to the brick at the edges, and mounded in the middle, and the temperatures are moderate, say in the 30's,, your house is reasonably insulated... well I would estiimate at least 10-12 hours burn,, and maybe as much as 14-16 hours.. there are just too many variables..
But as mentioned above,, a deep fire, don't poke at it, with the 'V' shape, this will guarantee clinker formation [my experience] just shake every 8-12 hours as needed, shake untill you see a few hot embers drop into the ashpan. The load the firebox up as full as you can.. As metioned above,, control your heat output with the air controls.. the more coal in the firebox, the easier it will be to control.. just the opposite of wood..
If you can find low ash coal.. I suggest UAE coal.. then with some practice and figureing out the right technique your unit should work fine..