Agree that there are many real-life factors , just wanna point out it isn't marketing material but from the aircraft support documentation. Engineers have calculated and probably also tested the numbers. 61 minutes can be done Probably without too much hassle and limitations.

OTOH, airlines "sabotage" it on purpose. For good reasons: They are not going to board 100 econ pax through J cabin.
And for bad reasons: light ticket fares that makes people bring their kitchen sink as handbag.

Also, some things might be costly: 3 different parallell catering veichles timed exactly. Multiple parallell cargo handling. And the jetbridges, boarding areas, multiple gate agents, multiple hose fuelling and so on