It can be short or very long indeed depending on the scenario in question. This is really giving no info way on the current game play (IE I really can't say something directly) but as a gamer (I love saying that) like many of you, I can assure you that you can have epic battles or fast scims all depending again on the scenario.
Is it a siege? how many defense are there, what are the numbers on both sides ? Are the defenses stone work or wood? Did you bring enough siege equipment? or has the defender put up a ton of trebs? Did you have to fight your way to their keep and loose units on the way? Did you get mercenaries to backup your numbers? What is the current experience of your troops overall? Are you going in green or elite? How are the defenders troops? Did he/she establish a range paradise? or did he/she go with Calvary for a sneak attack when you are not looking?
Maybe the attacker is going for a resouce hit to knock out all resources then make a run for it? Perhaps it's a counter manuver for an ally that is really after your other alliance member and this is a ploy run? Does he hold his attack longer then usual? Do you go out to meet him? Do you give chase to only be countered by another force? In the scale of EPIC , I have no doubt you guys will enjoy what you see here.
The questions and answers are endless, you won't be disappointed
So the answer is yes, epic long battles and short as you would expect in pretty much any game you have played. I like to think of it as BFME2 meets Stronghold = awesome baby
Thou again these are "my personal opinions" and in no way reflect those to Reverie World Studios, 505 games or any subsidiarity there in. (always got to throw that in there! Thou I am sure a few here agree