I'm not a Cowboys fan. Or even an NFL fan. A company I worked at bought us all tickets to go as part of a team building effort and I found the tour more interesting than watching a football game there. I did, however, really enjoy going there to watch the NCAA tournament when it was there a couple years ago!
It's a neat building. The tour guides seemed knowledgeable and acted professionally. They had a lot of neat details of the construction (like the 2 giant beams that span the length of the building dropped something like 6" when they hung the TVs from them).
I think we allocated 2-3 hours. It's been a few years since I did it.