No.
Weir went to his aid, and it was already over with.
This 'fifteen minute critical window' crap comes up now and then...
In the first place, Custer was far enough away that a fifteen minute hard ride would be a bet. And stretching out his forces in a mad dash would have been suicide.
Second, Benteen was currently aiding Reno, who had just got his butt royally kicked, too, and was discovering the hostile forces were much bigger than they knew.
Thirdly Benteen was protecting, and waiting on the supplies which included much needed ammunition. Had he gone, the relatively unprotected supply line would have been vulnerable, and he'd have gone in against an immense force under-supplied.
He dug in on Reno hill and waited for Terry... And probably saved all that were left.
It sucks, but it was probably the right thing to do.
