I know that you are anxious to know, but don\'t see any reply ......
I know you want to get it done tomorrow! I have not gone for PP stamping, but here is what I know of it. At Newark, Wednesdays are reserved for people with appointments (ie, people with letters like you have), so it will be less crowded on Wednesdays. They do stamping on other days too, but do not give any preference to you. This means more crowd, means longer waits, means have to go early. I have heard horror stories where people started lining up after midnight. So, if it is not really inconvenient, then I feel it is better for you to go next Wednesday.