Feeding cows in the evening, instead of in the morning, will cause the majority of calves to be born during daylight hours. Not everybody does it, but it works.
Research done at Kansas State University over a five year period, involving 537 births, documented 85.4% of calves born between 6:00 a.m. and 6:00 p.m., when cows were fed in the evening (between 4:00 p.m. and 6:00 p.m.).
Many studies have been done over the years, with similar results. Nobody knows why it works, only that it does.
Why do we care when calves are born? We care because difficult births are more likely to be detected, and assistance provided, during daylight hours.