Hi Alec,
this is just my 2 cents opinion of course:
I don't know (and we will never possibly know) whether Schneider ever ordered a "rapid fire" just after his Gabellgruppe.
I trust Jasper official report, that says he did order "rapid fire" after the Gabellgruppe against PoW (the second one).
He also stated that
PG could achieve a RoF of 27/28 seconds (2.18 spmpg). . However, during the whole battle,
PG had an average RoF of 1,64 spmpg.
The theoretical RoF of the German 203mm is 4 to 5 shell per minute per gun, therefore PG achieved a max RoF that is half the theoretical one (but an average that is one third of it).
I have tried to fit the number of salvos as per Marc definition (5 to Hood, 8 to PoW, until PoW turn against PG, other 20 to PoW until 6:04:30 when turrets are wooded and other 20 to PoW until cease fire (20 are needed to order 184 shots with 2 turrets bearing only.....).
This fits with Jasper declared RoF of 27/28 seconds, uniformly distributed and fired almost "metronomically" after the second Gabellgruppe. I don't see much space for slowing down (or accelerate) this RoF based on the total number of shots fired (136 after the second Gabellgruppe), on the account of Jasper (he says Albrecht did continue to fire rapid salvos from 6:04:30 (end of first turn) until the cease fire (6:09)), and on the tactical situation (Jasper had no reason not to continue a rapid fire after his order).
The theoretical RoF of the Bismarck guns was 2 to 3 spmpg, and
Bismarck achieved an average RoF of 0.93 spmpg, one third of the theoretical one, as it was the case for PG.
Based on that, assuming the same initial firing procedure (Vollsalve and Gabellgruppe with just a slight correction to switch target without repeating the procedure), I would conclude that Schneider could still have ordered rapid fire, but that the ship fired at a "practical" rate of fire.
Regarding the moment when Schnieder could have ordered the "rapid" fire, I tend to trust the Baron, even if a witness like F.O.Busch (in the main director with Jasper and writing his 1943 book much earlier than the Baron, wrote that Jasper ordered rapid fire against Hood....

. Possibly he was still looking at Hood through his binocular and he did confused the sequence of the events.....)
Bye, Alberto