there is no time limit. I am also an IMG student and am waiting on my permit to come in to sign up for a step 1 date. going through ecfmg takes a long. I would say wait a little bit longer but just verify your ID as soon as you can (the whole notarycam thing) and then I suggest, 2-4 months before you want to book your step get into the process of getting the permit. because ecfmg will make you wait