Bring the printed infopass confirmation letter, be there 15 minutes ahead of time at most, or 30 minutes late at most, otherwise they won't let you in.
If you don't need the stamping, you can just wait till you get your real card. The purpose of their taking your biometrics is to make you a card. So passport stamping is not a must. But it is as good as your real green card, valid for a whole year. So if you want, just make an appointment with infopass.
Good luck.