does each hive have a distinct alarm pheromone ... & duration

Curious question.

I believe that alarm pheromone is precisely the same, throughout the Apis mellifera species, and no different chemically, despite the subspecies or hybrid makeup of each colony. What is different, is how various colonies, or individual honey bees react to that pheromone. Some colonies, especially some that are AHB hybrid colonies, will have more of their individuals respond to the pheromone, and to lower levels of that pheromone. A level of the pheromone that might go completely unnoticed by EHB colonies, might attract the attention of, at least a few AHB bees, or Apis mellifera mellifera, bees, but then, of course, their attacks will add their own pheromone to the location and the race is on.

When working a yard of bees, I avoid the most defensive ones until last. That way the rodeo often does not start until I open them. If you work the mean one first, the rest respond to the chemical signals and things are hopping all the way thru the yard. That is why the two ornery hives I have in mind will receive new queens as soon as I have them.

>if a bee from hive A stings me, do bees of hive B close by pick up the released alarm pheromone... and act on it?

Yes. Depending on how sensitive they are to it, which varies from hive to hive.

> also, is it known, roughly, how long the alarm pheromone of a bee lasts (understood: it all depends on circumstances... but anyhow)

I would say, judging by my experience, days at least. Maybe weeks.