It will heavily depend on your server/battle-group.

As I posted somewhere else, I have been levelling my 5 Mages from 74 all the way to 80 without being able to enter a single Alterac Valley. Not one ! I was constantly in queue, played at different times of the day and night, etc ...

With constant rested bonus and 20% XP bonus from Heirloom, questing goes quite fast though.