Oral arguments are just one small part of what the Justices do. Mostly, it’s to review cases and discuss them with their law clerks and the other justices, and then review and/or edit draft opinions written (or sometimes write them, depending on their relationship with their law clerks).
I bet all 9 justices read all 2,200 pages of the bill before them. I’m sure they all cross referenced each citation as well.
Following that, I bet they read every brief and position that lawyers have presented for and against.
I’m confident they know what is at stake here.
(sarcasm)