Who would expect 9 crew members to maintain watches for 24 hours a day over the course of a 30 day patrol?

Russian subs are known for their automation, they were more automated than western subs. An operational crew of 3-4 with 8-10 hour shifts would make 24 hour operations no problem at all. With one person to steer the ship and one person to command the ship, you just need one person on sonar and one to control weapons. Loading of the Torpedos is automated so it isn’t like you need 5-10 guys to man handle a torpedo into a tube.
In addition to the 9 man crew there is room aboard for 6 combat divers so if you wanted to operationally man the vessel 24/7 then you could use the diver accomodation to man the sub for a patrol 24/7 if you needed.

You hardly need a Scotty to manage hydrogen/oxygen fuel cell systems.

Note that the midget subs like Piranya have crews of 4 or so and carry diver delivery vehicles like Murena for the swimmer delivery role, why build a mini sub if you just want to deploy divers? Any Typhoon class can fire a 533mm torpedo so can launch a Murena swimmer delivery vehicle, the point is that a mini sub can get much closer to the coastline than a full sized sub, while a midget sub like a Piranya can get even closer. In places where the water is very shallow normal subs can’t operate effectively, hense the purpose for both mini subs and midget subs.