It could be because of the sword, yes, but the timer was displayed after he stabbed him with the knife before he had the sword. Unfortunately, [Auto Mode] has shown that it functions outside the normal boundaries of logic, and could easily dive into a kind of paradox: where the reason it's that short is because of the sword, but he doesn't have the sword, so it's only by activating it that he's assured to be in the right place to obtain the sword, and thus the timer becomes its own self-fulfilling machina.