Only 72 Players can be in any given instance of Zadnor. It will never be higher, make sure you get 25 Clusters to get the riding map. That way you have max mount speed and can catch up to the train when it's running from Fate to Fate. Zadnor z3 Fates are all next to each other in a tight circle, if you have progressed enough, I think Mettle Lv.22 You will have access to Zone 3 via the Save the Queen Story, and you'll have no issue.

If you are farming mettle, the Fates are not the way to go as they give extraordinarily little. You'll want to farm Critical Engagements or the large Raids that will give you at least a level and a half of mettle each time.