Relaxed zone 2 time, which some experts say should make up about 80 percent of your training, is crucial for building endurance: When your goal is to log time rather than distance, you’re less inclined to rush through your workout just to hit a certain mileage. “If someone wants to run their first 5k but doesn’t have a specific time goal, then I would write a plan around the estimated time that we’ll run it in,” he says. For example, if you run a 10 to 15 minute mile, the run would take 30 to 45 minutes.