It's the »let someone else deal with it«-aspect, that makes the thought about time to install weapon systems realistic. It's not just »plug'n'play«. If you want do to these things properly, it will take a few hours. On the other hand, nobody ever maintains the crafts and weapon systems. So I tend to think, that nobody gives as hit about this little aspect. ;-) Otherwise that stuff would have to be checked in regular intervals. And every pilot would welcome that, as the worst thing would be an unexpected defect in a combat situation. But that also means, the crafts would have to be unavailable from time to time, for a few hours up to days, if the big checks are performed.