had known the hour

"had known when"

he would not have let his house be broken into

This can be stated in active form. AT: "he would not have let the thief break into his house" (See: rc://en/ta/man/translate/figs-activepassive)

The only similarity between a thief and the Son of Man is that people do not know when either one will come, so they need to be ready.

"do not know at what time"

Jesus is talking about himself. AT: "when I, the Son of Man, will come"