It can be hard to stay awake this time of year. Every day the sun sets a little earlier, and when it’s dark around 5 p.m., it can make 6:30 feel like midnight. Your body is naturally equipped to shut down when it gets dark. It starts producing melatonin, so you get sleepy and crave bed. But a couple of weeks ago, we learned that going to bed too early can have health implications. That study found that there might be a sweet spot for falling asleep. Falling asleep outside it, either before or after, may substantially boost the risk for heart disease. The research, published in the European Heart Journal—Digital Health, indicates that going to bed between 10 and 10:59 p.m. coincides with the lowest risk for heart health. The risk went up by 12 percent for those with bedtimes between 11 and 11:59 p.m., and more than doubled …