The AA fire does not go out in an hour or two of no call for heat.. I flipped my boiler off while I was working near it two days ago.. 36 hours later I looked in the boiler building, and noticed the water temp was only 140, Hmmm. then I remembered the switch was off, flipped it on, and 5 minutes later the fire was at full temp and the water recovered in another 5 minutes..
Unlike a flat-bed stoker like your Poccano, there is quite a bit of coal burning, and there is air being pulled through and over the top of the fire all the time, even with the fan off.. so you won't loose the fire easlily,, maybe after 2-3 days.
I run a timer on my AA in the warm weather, 2minutes once an hour..
I'd HIGHLY recommend installing the boiler, use it for a season or two,, THEN decide if it's a keeper or not.. I doubt you will decide to sell it..
BTW: if the coal is good, and you use DHW once or twice a day,, there will be very little unburnt coal..