That's because you don't alter your sous vide cooking times based on weight, but by thickness.
Some good resources / information for you to get started with:
You can also see different cooking times for different cuts of meet (I like to cook my pork ribs for 36 hours, for example). The tenderness of the meat really varies with the cut, so some of these you're going to cook longer to get the tenderness you desire.
Temperature determines level of doneness, but time makes sure it's cooked all the way through and to the level of tenderness you desire.