Preface:  I am cooking a private dinner for 14. Americana themed, surf and turf is what they asked for the main entree. I want to cook bison. The only cut I could find in town in time was a tri tip. $15 per lb. So $60 later, roughly 4 oz. per person.   Requirements:  I want a perfect medium rare.  Tender/melt in your mouth bites.   My questions:  How do I obtain that maximum tenderness texture.  How long do I sous vide for? Is there a significant difference between beef and bison?  I have 24 hours to play with the protein.  And I'm open to any suggestions.  
Medium rare tri-tip can be achieved using a water bath at 130 - 135F (55-57C) for at least two hours and up to 7 hours.  You will probably not get "melt in your mouth bites", as bison tri-tip is a leaner cut, but it should be quite tender if it is sliced against the grain. 