Just a note: the graduation times program give are often what they 'aim for', i.e. 7 years or 7.5 years. This may not reflect the current average - sometimes it is off by ~1.5 years! Some programs may claim that there are changes in the program structures that are not reflected in their current graduation time average, and state that the current averages are not relevant. While this may be the case (there will most likely be a modest decrease in time), unless you see clear areas where consideration has been given to time issues, or larger institutional cultural changes, I would be somewhat skeptical. Simply inquire specifically about current times if it matters to you (it really should to some extent, in my opinion).
It is more important that there is institutional acknowledgement in the md/phd program and within the medical and graduate school that length of time in an md/phd program is something to be considered and regulated in some manner. It is up to you to find out how aggressive or hands off they are about it, and what you are comfortable with. Notable programs have been rebuked for both allowing students to languish in grad school resulting in extremely long graduation times, and others have been chastized for pushing their students out innapropriately. Intelligent people have myriad opinions about how much regulation is too much, and whether md/phd students should be treated differently from graduate or medical students.
Finally, it is up to you as a student, to some degree, to be vigilant about these issues - while good programs will note where you are and how you are doing, there is no hour glass with your name on it at a program offices desk. Realize that every student is different and stays in a program for shorter or longer times for various reasons, some factors are within their control, and some are without. Perhaps we hold these truths to be self-evident, but nevertheless I thought it would be worth mentioning.