How I look at the Sunday test is less of a "are they like me" and more of a "will I get along with them many hours a day"? We work anywhere from 7 hours a day, up to 18 (especially during major code pushes) - we try to avoid this as much as we can, but sometimes (for us at our stage), it's inevitable.
I do have to enjoy working with my colleagues, and someone for whom I won't be willing to come in on a Sunday has a higher chance of bringing me down on a regular basis. That doesn't mean we work Sundays (we're typically in the office M-F), but it's important to be able to get along with people and it's a good litmus test, imho.