If the altitude is reduced to a point where sufficient oxygen becomes available again, how soon would people start to regain conciousness
That depends on the amount of time spent in an oxygen deprived state, and the physiology of the actual person. Reinhold Meissner could climb Everest without supplementary oxygen, I would probably die in 15-20 minutes if spending any time above 8000m.
Losing consciousness is the body's protective mechanism, shutting down the massively oxygen-dependent brain and keeping up a slow circulation to maintain basic life functions - for a while. Beyond a certain time the process becomes an irreversible coma soon followed by cardiac arrest.
Assuming a 2000/3000 fpm descent, from 35k ft the aircraft would descend to an altitude that is capable of sustaining life in under 5 minutes, and in under 10 minutes to a level where full consciousness can be regained in a matter of minutes. However if there is any extended time spent above 8000m (that is more than max 5-10 minutes), then the answer is probably never.
Looks strangely like a ship...
Because it is a ship, nothing strange about it. There is a smaller vessel docked to its port side.