While the effect of cows milk harvested at different time has not been tested on humans up to now, taking melatonin drugs has been suggested to those who are struggling to fall asleep at night.
请问这里的 time 为什么不用复数?
应该是 at different times(用复数的 times),因为不同的 time,肯定涉及多个。
另外,你的句子中的 cows milk 也有误,应该是 cow's milk。