Not long but, it would be determined by the size of the opening. The Black Sea was estimated (Ryan & Pittman)to have risen at the rate of one foot a day when it broke through at the Bosporus.
During the Ice Age the oceans of the world were reduced in depth by 300-500 feet, most accept 400 feet.
Go here and see a map of the world with the ocean depth reduced by about 300 feet. Notice that the Mediterranean Ocean is divided into three sections even at 300 feet. There are underwater scouring marks on the ocean floor that indicated a large intense flow of water ...just like at the Black Sea...at the Gilbraltar entrance
I do believe the Mediterranean was dessicated (lower water level) prior to the Ice Age melt.
The Mediterranean has been completely dried out at least 40 times, the last time was 4 million years ago. There are salt deposits on the bottom of the Mediterranean that are a mile thick and it is salt that forms only when exposed to direct sunlight. So... The guy has a good plan for Atlantis,at least regarding the water.
I have a theory that the same thing happened to the Gulf Of Mexico during the Ice Age. (That's how a city got 1/2 mile underwater off the coast of Cuba, another potential Atlantis site)
