How does Jesus not know when He is to come, but the Father only?
This is because Jesus was using a wedding idium. Notice the disciples did not question what Jesus was saying. They knew what Jewish weddings were like, and they understood completely what He was talking about.
You see, when a marriage is arranged in Jewish culture of that day, there is a betrothal. This betrothal is as binding as being already married. This is what our accepting Christ into our heart is, a betrothal. The bridegroom gives gifts of promise that he will return, which is what the Holy Spirit is for us. When the bridegroom leaves, he goes to prepare a small house built onto the side of his father's house where they will live. Jesus said, "I go and prepare a place for you." The bridegroom continues to build under the father's watchful eye. The bridegroom cannot stop until the father sees that everything is perfect and ready. Then the father says, "It is done, go get your bride." The bridegroom then rushes out, at a time unknown to everyone else, and comes in to "steal the bride away" to the marriage supper that is being prepared.
So you see, Jesus was speaking in a wedding idiom so that the disciples could picture what the marriage supper of the Lamb was going to be. A wedding between He and the New Jerusalem--the Bride.
