They DO state that they are taking on new staff AND reprogramming the whole thing.
This makes me thing 24 hours was a massively low estimate, and they just couldn't get the work done. How many I.T. projects don't come in late? ..answer is, almost all of them, especially those with 0 fault requirements.
You hear what you say? Good development not need to shutdown the live site. They not have a test environment and when the new code is ready and tested just will update to the live server? Of course it is possible to stop the site for a while but not so long as you try to say.
The reason they took it off line is that they discovered an issue that would allow an exploit! That is why the production system is offline. To be safe with everyone's coins and trades they could not leave the existing code running, so they halted the trading engine where the exploit vulnerability was. They have been rewriting the engine and testing, on what environment I don't know, I would assume a development machine.
Occasionally they will probably be pushing the code to the live server to test, and make sure any required new dependencies are in place. Until the testing has been run successfully and they are fully confident there are no other vulnerabilities, they will then bring the trading engine online.
Now why the whole server is offline for such extended periods, this I'm not understanding why. These various ups and downs of the server are a large part of the problem for people in withdrawing their coins. But as the devs have said there have not been a lot of hung transactions, and personally I've had no issue withdrawing or depositing.