en_tn/luk/12/39.md

(Jesus continues to tell his disciples a parable.)

because you do not know the hour when the Son of Man comes

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.

when the Son of Man comes

Jesus was talking about himself. So it can be translated as "when I, the Son of Man, will come."