He was even with the left front wheel of the follow-up car when Kennedy was hit in the head. So he was never close to saving him.
Hill was inches short of the left front wheel when Hickey fired his last shot of his accidental auto burst of at least 4 shots, ie at Z312.
Hill might have been in mid-air when Hickey fired the first shot of his auto burst, ie at say Z297 (if 6 shots) or Z303 (if 4 shots).