check whether it is issued with a validity date... usually, it is valid for 6 months, but you never know when you will get ITA, so I advise to get it after receiving ITA as it is just one-time/ one-day process and issued at the passport office itself on your visit and handed over to you there and then. Anyway, you have a lot to do before even thinking about post ITA documentation. First, let the ITA come and then go ahead step-by-step