I think it was implied but when you talk to your DVC Guide (salesperson), you can let them know that you only want to spend "X" amount of time on the tour and they will work to your schedule.
I think that the best scenario before taking the tour is that you know how DVC works and have all your questions asked and answered before taking the tour. That way, the tour is simply a walk through of the accommodations and a feel for the layouts, etc. If you aren't asking a lot of questions about how DVC works, there is no reason it should take a long time.
One other thing. Sometimes, Disney offers an incentive during a tour, and they usually only give 72 hours for the person to accept. So again, the tour is best if it is the last item on the decision list so you be ready if anything is offered. I'm not saying that there will be a special incentive, but if there is you want to be prepared.