To take the exam on a Sunday you need a solid reason such as religious reason and it is something you have to "apply" for I believe.
If you are active on the MCAT forum of SDN you will see when AMCAS opens registration for the MCAT before most people are aware of it. This gives you a good shot at getting THE BEST location.
I reviewed the site Arsenic showed and picked what was ranked as the best location and had nice comments, nice table space. It was in a BIG hotel but from what the test administrators said it is the same group of people administering MCAT exams at this site and this was the most demanded site in the NYC area. They knew what they were doing, were very efficient, and we got out earlier than expected. Bathroom breaks were low stress. Lines may be 3 minutes long but so what. They give plenty of time for bathroom breaks.
Pick THE BEST site. Not some crap site with clueless unorganized test administrators or a place where the air conditioner will break because its a crappy hotel and the repairmen suck there,etc.
Hell during my lunch break I had a nice walk on the NY riverfront of battery park. That place is beautiful. Made me forget about the 10 questions I did not answer on the PS section.