They take forever. Last year, I planted early in the spring (March) and did not get any of a proper size until nearly frost. I planted others last fall and they developed nicely this spring. You are probably colder than I am so I don't know if it would work for you, but I left some of the grown ones and the newly started ones in the ground over winter, covering them when it got into the lower 20's. They did great. From now on, I plant leeks in the fall.
Don't forget to pull the dirt up over them to blanch them. I did not do this on my first ones until they got pretty big and it still worked out well. I don't know if they would have grown faster if I had done this.