This likely totally depends on players (and, partly, classes and groups). There were players before rocketing chars to 20 in 1-2 days, formerly by searching out mobs and grinding them, in the Beta a good group for events and quests like colossus (still no clue where that one even is) likely also helps.
As a musky I got around half a level in 4h, went from 8 to 9 LOL. For 2h after launch I was testing the dungeon, 2 more hours I hunted some green questmobs - takes forever to bring only one down -, fired my critter gun at critters a bit, explored and went to the two events I saw without completing them because there weren’t enough people around.
Today I wanna check out the pala, level the bard further and - perhaps - try to get the musky to 15 to have relocate turret already, but I doubt I make it in one day and I also doubt leveling is too fast, for the vast majority of people, also considered these chars are wiped anyway at some point.