You can do it in about 9 hours, using this path. I like to keep the travel to a minimum, it's just not worth moving instances every 5 levels.

10-20 SFK
20-45 SM (I've found even though 41-45 is slow it's faster than moving instances)
45-55 Strat
55-60 Underbog

You could probably do 55-60 in strat instead, the underbog pull is much much harder, but the mobs give over 3x the xp per kill.