2 minutes between captain returning to cockpit before he realizes the problem.[1]
02:11:43 (Captain) What the hell are you doing? [captain returns to cockpit]
02:13:40 (Bonin) But I've had the stick back the whole time! [At last, Bonin tells the others the crucial fact whose import he has so grievously failed to understand himself.]
Note that at the point of the transcript you're referencing, the captain was in the cockpit but not seated at the controls. It therefore would make no difference to his awareness of the situation whether or not the control sticks were linked, as he wasn't holding either of the sticks.
Unlike the captain, the PNF and PF (who were seated at the controls) both seem to have thought that they needed to climb. See 2 h 13 min 39,7 and 2 h 13 min 40,6.
Of course the official accident report is a better source, but I’m not arguing linked controls would have helped. Just that it took the captain a few minutes to grasp the situation.
The senior copilot was in the other seat, and the problem was that the unlinked controls meant that the senior co-pilot did not know during the previous 10 minutes what the junior Copilot Bonin, who had the controls, was doing, and that his (senior copilot) input to put the nose down was doing nothing
Unlike the captain, the PNF and PF (who were seated at the controls) both seem to have thought that they needed to climb. See 2 h 13 min 39,7 and 2 h 13 min 40,6.
There's also evidence from the rest of the transcript that the pilots at the controls were perfectly capable of observing (or inferring) which inputs were being made.
I think there's an underling misconception here that an Airbus sidestack has a "position" akin to the position of the yoke of a plane with fully manual controls. An Airbus is flown with the sidestick remaining in its central position 99% of the time. To climb, for example, the pilot makes a short backward movement and then lets the stick return to its neutral position. The flight control software will maintain the specified climb until another stick input is made. For this reason, stick inputs tell you very little. If, for example, you see the PF push the stick forward, that doesn't necessarily mean that the plane's being put into a dive. The PF might just be reducing the rate of climb. You'd have to keep track of the complete history of stick inputs to know what was going on.
On top of that, as only one pilot has their hands on the stick at any given time, for the PNF to visually observe brief movements of their own sidestick would hardly be any easier for them than just looking at the sidestick of the PF, who's right next to them.
At 2h 10m the PNF (copilot in the left seat) warns the guy on the right about speed and says he needs to go back down. I believe that this is where the issue is, where he doesn't realise that the guy on teh right is still trying to climb. I think this is something I also read in the article, and it's good to see it in the logs (thanks for posting them)
It wasn’t until a few minutes before Air France’s crashed that the pilot realized what the copilot was doing.