The impact will really depend on what points in the construction the decks were that burned, and the decks that got smoke and water damage.
Not only do they need to redo the lost work, but they need to clean up the mess. Have engineers determine if the heat from the flames will require any structural rebuilds as steel is damaged by extreme heat. It will most like be at least a month, and probably 2 months before a full impact is known. Insurance and saftey inspectors are also going to want to do a fair amount of study before things can progress again.
Throwing more workers at it is probably not going to get the ship off on schedule.
Good news is that they must have good saftey procedures to get all the workers to safety. Good job.