I have seen applications go from submission to hiring manager review to hiring session invite in a single week. I have also seen applications sit as submitted for months, then sit as hiring manager review for another 2-3 months before a hiring session is finally scheduled. It depends on what terminal you are applying to, and who is handling the applications, how bad they need people and such. If they are in immediate need of people it will move quickly. If they are not even sure on how many they need, you might sit at hiring manager review for a few months. You just never know how long its going to take. The railroad has it's own way of doing things at their own pace. Only thing I can tell you is sit tight, get comfy, and wait.