Luke 12:39-40  But understand this: If the owner of the house had known at what hour the thief was coming, he would not have let his house be broken into. You also must be ready, because the Son of Man will come at an hour when you do not expect him.”

Here is what this sounds like to me…

Satan is the current “owner” of the house.  Jesus has to come at a time when Satan does not expect him. Satan is much smarter than we are, so if we were able to figure it out by any means that he has access to, he would have figured it out long before we did.

Therefore, the only way we will know will be through a way which Satan does not have access to — by the Spirit.  It will be something that we will feel, but will not be able to figure out by natural means.  It must be spiritually discerned.

So Jesus is saying:  “I can’t tell anybody when I am coming, because then Satan would be able to figure it out, so you will just have to be ready.”