This side quest only exists in Enhanced Edition of the game, in original version of Baldur's Gate, Kivan will stay in the party no matter how long it takes the player to reach the Bandit Camp. This companion quest starts as soon as Kivan joins the party. As it's earliest available from Baldur's Gate Chapter 1 but can't actually be completed until Baldur's Gate Chapter 4, it's advised to time your progress or Kivan leaves if you take too long.