There's a shocking amount of misinformation going around here.
Mormon missionaries have a highly regimented schedule that controls when you wake up and go to bed, when you study, how long you eat, where you can go, who you can talk to....you get the picture.
6:30 to 7am is the time allotted for exercise. Now let's keep in mind of couple of things here. Missionaries have to wake up at 6:30am everyday for two years(barring major illness). EVERYDAY. There's no saturday sleep-in session. I can assure you all from experience that you don't exactly jump out of bed at 6:30am every morning under such circumstances. Now, let's say that you actually woke up on time, you are now faced with many other issues. You are probably extremely sore and depleted from walking an average of 6-7 miles the previous day in dress shoes on third world asphalt roads. Sounds easy? Try doing that for one year without ever taking a break and tell me how your body feels. Next you get to deal with the general lack of body energy and power which can be generally attributed to sub-standard foreign diets. I ate meat maybe once every two weeks. Half the time you are scraping by just barely financially and sometimes have to skip meals to save cash(remember missionaries pay for their mission, they recieve no salary).
If you actually are motivated enough to brave and get yourself out the door to run, you now face the BIGGEST obstacle to beneficial running training. Your missionary partner. Missionaries are never allowed to be alone. You always must have your serving partner within sight and hearing at all times(except bathroom obviously). So unless you are serving a mission with another D1 collegiate runner(highly highly unlikely), you can either force your overweight partner to run your pace, or you can run his pace. Which one do you think is most likely to happen?
Remember you have only 30 minutes.
Not to mention you spend all your time and energy serving and helping people, learning a difficult language, and enjoying a new culture that you generally start to lose interest and focus on things that don't ultimately matter in life(while I love running, God doesn't care what your 5k time was).
On my mission I maybe ran 5 times over two years. It was just for fun, and yes, I ran my partners pace, so it was practically walking. But even if I had found myself paired up with some all-american XC runner, I was so malnourished and tired from the enviroment, that I think anything more than 10 miles a week would have killed me.
That's seriously the condition you are looking out. Anyone who thinks taking two years off to serve a mission will give them an unfair advantage in collegiate sports is seriously misinformed about what missionaries actually do. In fact, I think BYU performs well DESPITE their athletes all having served mission. That can only attest to their great coaches and training.
Hope you enjoyed my post. I'm sure someone will be angry and call me a cult-heretic, but I needed to explain the overwhelming information dichotomy in this thread.