I presume even if they start now, it will take hours to get it truly plugged.
As fast as the water is rising, it won't make much of a difference whether they fix it or not.
Didn't we know about this since the middle of the night? Why was nothing done?
We don't know that "nothing" was done, nor do we know if it was/is even possible to do anything.
My guess is that the water will not rise any further. Everything below sea level is under water, and the water in NO is even with the water in Lake Ponchartrain. Canel street is about at sea level, rising to five feet in the last few blocks near the river, although the topo maps are 20 years old, and NO may have sunk a bit.
You can't fix a leak like this until the water stops rushing in. I would guess that even 3000 pound sandbags will do nothing but get washed away.