Benjamin honestly came as soon as he could, which wasn't that soon. Which definitely was not nearly as soon as he would have liked, but there were people in obvious life threatening states that needed tending to, first.
He did eventually make it to the boarding house, where he was directed to John's room, and he immediately told Ms. Blackwood to go fetch him some hot water, if she could. Without a word, he pulled the blanket off John to examine him, and did not in fact wince at the open fracture. He was a doctor.