While I made a small comment about this before, I think that its rather clear from the actions of the typical Witness that they don't really believe that Armageddon is imminent, rather I think that they are 'hoping' (at best) that it's coming soon. Why do I say this? Well, if a person really believed in something with 100% certainty, that person wouldn't have a plan 'B'. But we see the typical Witness go on regular holidays, take out mortgages and lead sort of normal lives, trying to enjoy both worlds. Of course, most Witnesses when asked say its just around the corner, but their lives really belie their claim.
On the other hand, whether Witnesses believe that they are living in the Last Days, I reckon most probably do. This is because, their simplistic understanding of world events and trends fit their belief structure. And in actuality, it a quite safe position because it mentally easy to attribute a disaster, a war or a savage crime, to this teaching. As compared to comprehend all the good in this world.