Is this a fun event or are you participating with the plan to podium? There is a big difference depending on your goals. I've never done a 100-mile MTB race, but I've done shorter ones. Speed can either make you or brake you on any endurance event. Too fast non-stop without resting/refueling/hydrating and you won't even finish half of it. I don't think there is anyone who does. On the other hand, I have met freaks of nature who only need very little water/food to keep going, but that's not me. Now, should you decide to kill time at every rest stop, most likely you won't finish it within the limit or will force you to ride into the night (increasing your chances of injury.) Many MTB events sometimes have more rest stops than necessary just to cover liability and safety issues. No need to stop if you're feeling strong, but you should carry enough snacks/water to make it to the next stop. I would view the rest stations simply as "pit stops": hydrate quickly, take a few snacks (if available) and water and keep going. Only you know at what intervals you need to stop for a more substantial meal, rest, etc. No matter what you do, remember that once you enter an endurance event the main goal should be to finish it within the time limit. To me that's what counts!