Matthew 24:33 does not assure us that Christ must return before 2020 simply because the bible is frequently misinterpreted and misread. A lot of people came to the conclusion that christ was returning in 2012 and obviously that didnt happen. I think that when the time is right Christ will return but the bible never says a specific day or year.
According to biblical scripture the return of Christ is not known by any man, living or dead. It is insisted upon in the bible that "no man will know when he returns, no the hour, not the day". So with that in my mind I do not believe Matthew 24:33 insists any such thing.
No I don't think that anyone knows the time out hour. I think we can have a pretty good idea of the estimate bit nope no one knows. There have always been people who give time and we are still here so they have all been wrong so far, likely it won't be centuries still