For PA to work on FB you need something to do inbetween ticks. People play FB games to have something to do while they are bored. Sending an attack, waiting 7hrs and then check wont be enough to keep people interested.
I m currently playing a game which is alot like PA back in the days ,amount of people, alot of new nubs coming constantly and alot less restrictions than PA these days. I havent played it enough to make up my mind yet, but I will actually make an effort to get used to it and get to like it.
Storebo thinks its alot better than PA, so he cant be all wrong!
I do think, that if PA had invested to get into FB as an app, it would be a great success. Only minor changes would be needed gamewise. Coding I dont know anything about.