I just finished my 5th 100/110-120 alt tonight, full heirlooms and the anniversary bonus make it take about 5 hours from 100-120, and around 3 to 3-1/2 for 110-120 in my experience. A lot of that is luck of the draw on if you win. I've been playing Alliance, or mercenary Horde as alliance, and have won about 60% of the matches I play.