This latter indication is the critical one in this piece. Actually the motion at this point becomes, to my ear, more turbulent. Not only are there turbulent triplets but the sudden emergence of lots of sharps and double sharps in intricately intimate counterpoint between the two hands seems to impart a tonal urgency as well.
After a long time of puzzling it out and then giving it some distance I realized yesterday that Brahms, a master pianist, had managed to write configurations so awkward as to require extra time to find and then cause the correct key to speak. The ear in this case takes a back seat to the choreography.
A great and deeply troubling work.