I'd just like to put the timescales mentioned here into perspective from a different type of software system. My experience of development has been providing online services in the form of web applications, so that means our customers don't need to install anything. That means our release process is different from the one mentioned in the question: it sounds a lot easier and quicker.
But any errors we introduce can impact the business severely, and in these cases 48 hours is just too long to fix a critical error. In such cases we need to take a view on how much the error is affecting our customers. If a high percentage of customers are affected then it needs to be fixed ASAP, but if only a small percentage is affected then a longer time can be taken to fix the error.
In our case it comes down to how much business we'll lose by not fixing the error.
http://devproj20.blogspot.com/2007/11/how-fast-is-your-turnaround-time.html
"Take that, you hostile sons-of-bitches!" -- James Coburn, in the finale of _The_President's_Analyst_