Conjecture: The amount of time it takes to use double crux as a group can be lower bounded by the amount of time it takes every pair to double crux. If we assume the amount of time for every pair is the same (which it isn’t), and call that amount of time t, then the lower bound is t*n(n-1)/2. (Because n choose 2 = n(n-1)/2.)
“How much time it’d take to pairwise doublecrux” seems like a useful detail, but doesn’t seem like either an upper or lower bound. (I think it works as “this is approximately how long you should expect things to take on average”, with some debates taking longer and some shorter)
Things might take longer, because maybe if everyone pairwise doublecruxes, each pair ends up disagreeing with other pairs due to idiosyncratic beliefs or personal-history that other pairs didn’t share.
Things might take less time, because multiple people in the group might share enough beliefs that they can functionally share updates.
i.e. if Alice, Bob, Catherine and Doug all doublecrux, it might be that once Alice and Bob have doublecruxed, Alice can easily say to Catherine (who has a similar worldview ‘Bob explained this to me, it works like X’, where X uses some shorthand that Alice and Catherine already share.