I bank In queenright hives, required to do so are a queen excluder, shallow super, and banking frames.
As for how long a queen will survive in a banking frame is anyone's guess. I would suspect indefinitely as long as the attendants continue to feed her. Which in most cases would also be indefinitely as nurse bees will generally feed any queen that begs, it is an instinctive response..
My concerns for keeping queens banked for an extended period of time would be in the realm of her prolonged productivity.
From time to time in my beekeeping carrier I have noticed that some queen were hard to introduce to the hive, their interaction with the attendants upon release seemed abnormal, and in many cases these queen failed prematurely, and were superseded.
It was not until I started rearing queens that I was able to correlate this behavior with queen that had been banked for extended periods of time. Although speculative I have come to believe that the stifling of egg production, along with the artificial relationship between attendants, and in combination with the presence of pheromones from other queen has an impact on the banked queen. which results in abnormal behavior, and production.
For what it's worth!