Willet championed the idea of Daylight Saving Time until his death in 1915 and never got to see it institutionalized. Germany was the first country to put Daylight Saving Time into place. On April 30, 1916 the country moved their clocks forward in an effort to save electricity during World War 1. They could leave the lights off just a little longer into the evening than other countries.
Although the logic behind the clock change was sound, our brains and bodies did not agree. Science has shown that our biology likes it much better when we synchronize our activities to the rise and fall of the sun. We need darkness at night when we are preparing for and then going to sleep. We need light in the mornings when we are waking up and starting our day. The duration of sunlight is greater in summer and, as Willet noted, we can block the sunlight from our bedrooms in the very early morning when we are still sleeping. Opening the window coverings allows us to get all the morning sun we need during Daylight Saving Time in the summer. The problem is that when we are not in our bedrooms later in the evening, we cannot block out the light as easily. Exposure to evening sunlight tells our brains and bodies that it is still daytime and time to be awake and not sleeping. We are out of synchronization with the rise and fall of the sun. This can lead to later bedtimes which usually results in less sleep or, if we do go to bed when it is still somewhat light out, the sleep we do obtain can be poorer quality.
Winter shortens the duration of sunlight. If we were to maintain Daylight Saving Time during the darker months, the shortened day would mean the sun would set earlier and we would be in darkness when we are preparing for and then going to sleep. Although biology would appreciate this synchronization, the sun also rises later and this means we would be missing the much needed morning sun. Standard Time corrects this problem. Moving the clock one hour back in the winter means that instead of sunrise occurring at 8:00 am in November, after most people are awake and starting their day, it will rise closer to the average wake up time at 7:00 am. This means our brains and bodies will be better synchronized to sun light. We will be waking up when our biology thinks it is time to be awake because the sun will be up, rather than getting up when our biology thinks it is still time to sleep because the sun has not risen.
You might be saying, but doesn’t Standard Time mean that the sun will also set one hour earlier at 5:00 pm instead of 6:00 pm and we won’t be getting sun in the afternoon when we are still awake? This is true. However, biology and electricity buffer the problem. Morning light plays a much stronger role in keeping our biology well-tuned than light later in the day. We sleep longer and better and our physiology runs more smoothly when morning light occurs when we are waking up. Missing a little light in the evening has much less of an impact on our smooth biological operations. Plus, when early evening darkness is telling our brains and bodies it is time to sleep during Standard Time, we have electricity to help. We can turn on a light and get just enough artificial light to keep us going. When we are getting ready for bed and then falling asleep, we can simply turn off the light and tell our biology to go to sleep. All this means that if you have to choose between morning light and evening darkness, light in the morning is better.
What will a change to permanent Standard Time do for us? One of the remarkable changes will be an immediate decrease in heart attacks and motor vehicle collisions right after moving from Standard Time to Daylight Saving Time. We lose one hour of sleep in the spring and this loss has been reliably linked to these negative outcomes. The next positive changes will be an improvement in our sleep. Better sleep, combined with improved synchronization to sunlight, will then lead to improved cardiac health, better body weights, a decrease in cancer rates, reduced alcohol and tobacco consumption, better psychological health and improved performance at school and work.
All of these benefits have led to numerous initiatives to scrap Daylight Saving Time and scientific consensus on the topic.
Footnotes & References
 Although William Willet is often credited as the inventor of Daylight Saving Time, is was likely first proposed by an entomologist named George Vernon Hudson from New Zealand: Institute of British Geographers Publication (1948). New Zealand Geographer, 4 (1), 104.
 Rishi, M., Ahmed, O., Perez, J., Berneking, M., Dombrowsky, J., Flynn-Evans, E., Santiago, V., Sullivan, S., Upender, R., Yuen, K., Abbasi-Feinberg, F., Aurora, R., Carden, K., Kirsch, D., Kristo, D., Malhotra, R., Martin, J., Olson, E., Ramar, K., Rosen, C., Rowley, J., Shelgikar, A., & Gurubhagavatula, I. (2020). Daylight saving time: An American Academy of Sleep Medicine position statement. Journal of Clinical Sleep Medicine, 16(10), 1781-1784.
 Kantermann, T., Juda, M., Merrow, M., & Roenneberg, T. (2007). The human circadian clock's seasonal adjustment is disrupted by daylight saving time. Current Biology, 17(22), 1996-2000.
 Merikanto, I., Lahti, T., Puolijoki, H., Vanhala, M., Peltonen, M., Laatikainen, T., Vartiainen, E., Salomaa, V., Kronholm, E., & Partonen, T. (2013). Associations of chronotype and sleep with cardiovascular diseases and type 2 diabetes. Chronobiology International, 30(4), 470-477.
 Roenneberg, T., Allebrandt, K., Merrow, M., & Vetter, C. (2012). Social jetlag and obesity. Current Biology, 22, 939-943.
 Borisenkov, M. (2011). Latitude of residence and position in time zone are predictors of cancer incidence, cancer mortality, and life expectancy at birth. Chronobiology International, 28(2), 155-162.
 Wittmann, M., Dinich, J., Merrow, M., & Roenneberg, T. (2006). Social jetlag: Misalignment of biological and social time. Chronobiology International, 23(1-2), 497-509.
 Borisenkov, M., Tserne, T., Panev, A., Kuznetsova, E., Petrova, N., Timonin, V., Kolomeichuk, S., Vinogradova, I., Kovyazina, M., Khokhlov, N., Kosova, A., & Kasyanova, O. (2017). Seven-year survey of sleep timing in Russian children and adolescents: Chronic 1-h forward transition of social clock is associated with increased social jetlag and winter pattern of mood seasonality. Biological Rhythm Research, 48(1), 3-12.
 Van der Vinne, V., Zerbini, G., Siersema, A., Pieper, A., Merrow, M., Hut, R., Roenneberg, T., & Kantermann, T. (2015). Timing of examinations affects school performance differently in Early and late chronotypes. Journal of Biological Rhythms, 30(1), 53-60.
 See for example the Canadian Sleep Society’s position statement: https://css-scs.ca/position-statement-of-the-canadian-sleep-society-on-the-practice-of-daylight-saving-time-dst/