“So you, too, must keep watch! For you do not know the day or hour of my return." (Matt. 25.13)

Who is this being spoken to? It is being spoken to the 5 unwise Christians who were not watchful. If they were watchful, therefore, they could have known. Even those who are watchful don't necessarily know; but being watchful is a prerequisite to knowing when He returns.

"Remember therefore how thou hast received and heard, and hold fast, and repent. If therefore thou shalt not watch, I will come on thee as a thief, and thou shalt not know what hour I will come upon thee." (Rev. 3.3)