in the early morning?

题目

in the early morning?
In the early morning,the food that had been laid out for the dead is thrown into a river or into the sea as it is considered unlucky for anyone living to eat it.
这里in the early morning为什么用in,
因为morning 前有形容词不是应该用on,on the early morning

答案

强调具体到某一个早晨用 on
这里的意思就是在较早的早晨