Will this double the withdrawal time?
At least it's better than no withdrawals. But i doubt they have the bitcoins to cover the current balances of their customers at this point in time. They're probably going to be doing arbitrage from their exchange to the others for a couple weeks so as to make back the money that the hacker stole. All under the disguise of 'waiting for a technical update'. Once they have made enough coins to cover their customers balances they'll probably implement a fix like this.
No, this shouldn't double the total withdrawal time since the first transaction can be regarded as "internal" transaction thus they don't need to wait for too many confirmations before processing to the next step. Plus there're likely many other factors that have much greater impact on the overall withdrawal time anyway.
Given what we know thus far, I'm very skeptical of the idea that somehow they became inadequate with their bitcoins or fiats to cover the customer payouts. Think about:
1. This is a company that makes a huge profit primarily out of running software on servers. Yes, there is development cost, operational cost, legal cost, banking cost, support cost and insurance cost etc. OK, perhaps not the last one. But if you check their daily exchange volume and their fee schedule you can get a rough idea of how much they're making every 7 days a week, excluding transaction fees.
2. Regarding the possibility of them being hacked, their main trading system actually doesn't need much direct interaction with the Bitcoin network Once the funds and bitcoins are credited to the exchange's user account, that platform can be fairly isolated from dealing with the Bitcoin network given all trades made on there are just account clearing activities.
3. The only time that they need to interact with the Bitcoin network is for receiving/sending bitcoins from/to external wallets.
4. A rather limited hot wallet should be adequate enough to satisfy such needs on most days.
5. The cold wallet really is just a set of addresses and an encryption key. They don't need to physically copy/move bitcions to there. Cold wallets can receive bitcoins while it's on ice (50 identical thumb drives sitting in different bank vaults).
6. With regard to the possibility of them being the victim of the transaction malleability issue, they had to be really stupid to lose a lot of bitcoins. That's assuming they were retrying failed transactions from different bitcion addresses every time one was emptied, or they were sending them from their hot wallet address directly without allocating just enough amount to a new address first and do it from there.
