C-12 autopilot activation can happen anytime over 200' and then has to be disconnect no later than 200' The yaw dampner has the same restriction but has to be on prior to going above 17,000' Usually you do not turn it on low while hand flying because you are still utilizing the rudder and you will lose some control over the rudder, making it harder to make inputs as needed. Personal preference on when you turn it on, all depends how good it functions, if it is in good shape the C-12 autopilot works well.