as far as i can see, there are 2 scholarly schools of thought.
1. in all jewish weddings, the son would answer (to any question about the wedding) 'i don't know, ask my father', like it was a cultural thing, special for weddings. so as the end of the world includes the wedding of the bride (church) to the Lamb (Jesus), He followed the jewish tradition.
2. Jesus, God the Son gave up some of His Divine knowledge in order to come to earth and be incarnate.
i wonder if maybe it is a bit of both, but certainly now He knows, but He won't tell us coz we'll just screw up.
it's better if we spend our whole lives getting ready, rather than find out it's going to be next year and just be complacent and spend all this year sinning.