He says he will be back —— 10 o'clock.为什么 用 at 而不用in?

问题描述:

He says he will be back —— 10 o'clock.为什么 用 at 而不用in?
如题
但是可以说 是 in a minute 啊

at常用来表示某个确切的时间点,而in却表示一个时间段,或在将来某个时间之前相当于within.
举例:
He says he will be back in the night.他说他会在晚上回来.
He says he will be back in (within) 3 days.他说他会在三天之内回来.