God closed the door of the ark seven days before the rain began to fall in the days of Noah. There is a good theory that I happen to believe is very possibly true that the major natural cause of the flood was a comet that struck both the earth and the moon and possibly even the sun. If this theory is true then the comet would have been seen approaching the earth closer and closer causing increasing fear and finally panic. It may be that the reason God sealed the door of the ark one week ahead of the beginning of the flood was to prevent anyone from trying to save themselves inside the ark based purely on motives of fear. If the only reason they entered the ark was terror of the approaching comet instead of faith in God's warning and His word, then they would only be a liability and a curse that would perpetuate the condition of overwhelming sin that brought on the flood.
As it was in the days of Noah, so shall it be....