All turns during flights under instrument rules shall be made at standard turn rate, but no more than 30 degrees of bank. In case of vacuum-driven instruments failure (i.e. directional gyro, attitude indicator) the rollout to new heading is timed: let's say the aircraft is flying 060 degrees heading and it needs to fly new heading 360. The turn will be 60 degrees. Since the standard rate turn is 360 degrees in 120 seconds, the plane will need 20-second standard rate turn to the left.