I don't have that much experience, but if you're Horde it's popping atleast every 5 min, a little longer if you're Alliance. Can't say much about when to queue, but guess it's the same as 19.
damn it , too bad i am moving to horde with my hunter maby we could have played together for once, but i guess we gona have to face each other on both fronts 80 and now 24
P.S. although we never rly face off on 80 coz our online time is not in sync.