Unquestionably that will be the day.

毫无疑问，就是那一天。

Eg. That will be the day.

有这么一天就好了。

That will be the day.

要有这么一天就好了。

That will be the day!

会有那么一天吗？

My husband, get up before eight o 'clock? That will be the day!

要我丈夫八点以前起床吗？那样的事永远不会发生！