Personally, I would urge exchange owners to require 144 or 288 confirmations (nominally 24 or 48 hours).
It is definitely too draconian. Imagine there is a sudden jump in BTC value and you want to cash out. Sorry, 24 hour waiting.
The exchanges can, however, instate a 24 hours waiting period for cashing out. Essentially, you could withdraw balance that was there 24 hours ago. If there is a BTC reversal, the perpetrator would have a negative BTC balance in the exchange account. The USD balance that is hold for 24 hours could cover the loss then.