You've got a long wait, largely because your chick is alone. I would say two months, then play it by ear. If you've still got snow and cold, or cold and rain, wait for milder weather. Try to get the chick a friend if you can. If you want to bring the adults in, that's fine, but set them up with a fence wall first (so they can see but not touch) and later a creep, not direct access. A creep is a wall that has gaps in it small enough that the adults cannot pass through but big enough that the chick can, like rails on a baby crib. Adult chickens can peck a baby chick to death. Observe them closely.