You can take the test on a Saturday. I am currently signed up for a Saturday exam. However, I dont know if this available at all sites. I would check the site where you want to take it, but look at the last month available on the calendar where chances are everything is still available. That way at least you can see whether Saturday is offered at all.
BTW, my test is scheduled in LA.
EDIT: Didnt read the second part of your post clearly. You can see the calendar without signing up. Your nbme id# is the same from when you took step 1 (thank you gmail search!)