With the cabin crew knowing the code, the only thing that gives the "incapacitated" theory still merit is:
there is a possibilty that an agitated captain misses his small time window to re-enter after the 5 minutes have expired
However I cannot see how this would work. Why would the captain
not be able to enter the cockpit after 5 minutes? The 5 minutes would just expire and there would be no 'small' time window, but an infinite time window to re-enter the cockpit. Until the ground was there obviously.
When did the 5 minute lockout start. That can be worked out from the CVR easily.