Normaly if you arrive too late or too soon in the day (that's often the case), you need to wait on the railing just in front of the entrance. The quest marker moves on the railing on its own (a bit like when you get to the clouds too early).
Off topic : Interesting the name if the quest is not the same in any language. In French & English, it's "M'ap Tann Pelen". I had to search for knowing what quest was it.