It isn't possible to know for sure how long the kill actually took on the bison but the shots were perfectly placed for archery---right in the area of the vitals (lungs and heart). That kill depends on blood loss which does not immediately put the animal down.
Even with a rifle where you have the added effect of high impact I have had a whitetail buck run close to 100 yards with his heart blown up.
450 fps is about 75 fps faster than my crossbow.
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