With all due respect, (I know you have spent a helluva lotta time there).
Boston Custer, I believe the General’s nephew, had time to pass Benteen’s command on his way to the pack train for a fresh mount.
He made it back in time to die with George and Tom on Last Stand Hill.
This was about the same time Benteen received the orders from Custer.
“Big village, come quick, bring packs”
I give Colonel Benteen a helluva lotta credit for what he did on Reno hill, he held that perimeter together. Reno was in no shape to do it.
But I still believe that he had time to reach, possibly save Custer.
He had no desire to help Custer. He thought Custer had sent him on a goose chase to keep him outta the fight
My take is that Reno choked on his charge, and lost his head completely after Bloody Knife’s brains splashed his face.
When Benteen got to Reno Hill he couldn’t give a schit about Custer.
Weir asked Reno, in Benteen’s presence for permission to go to Custer’s aid.
With no answer, Weir went on his own. His company, and eventually the rest of the regiment, followed. (Probably to save face).

"Preserving the Constitution, fighting off the nibblers and chippers, even nibblers and chippers with good intentions, was once regarded by conservatives as the first duty of the citizen. It still is." � Wesley Pruden