My fastest time is 10-12m as a Human.
Needed:
Elemental Force Weapon for all classes except hunter. Scope of doom for hunter/doesn't really matter, hunters 2-shot everything anyway. Armor heirlooms aren't necessary, an heirloom weapon with elemental force will 1 shot everything before it has a chance to hit you, up to level 9.
I do keep a set of white cloth gear with Assault enchants on them, as well as one with spell power enchants. They don't soulbind and they can be mailed to any character.
I make lots of level 10's for open bracket twinking so this information is good.
-Go into /who and start whispering for guild invites if you don't get one automatically.
-While you're searching for a guild, just kill every mob on your way to every rare spawn in elwynn,
-I start at the rare wolf north of Crystal lake, head east to the spider cave, go to gnolls around the lake north of the lumber mill, head south to the fox/turtle, head west to the defias bandit, head north to the other defias in the cabin by the lake northwest of goldshire. By this time I'm usually 10, but if not I'll just grind random mobs around me, or head to the gnolls south of the bridge to westfall for the rarespawn that is there.
Here's a comprehensive guide on low level enchant scailing and effectiveness:
[US+EU] 5.4 Enchants Shortcut