Rotation for set time?

Hey all how can I make the following turn to a certain point then stop turning?

transform.Rotate(0, turnSpeed * Time.deltaTime, 0 * Time.deltaTime, Space.World);

reason being is that this is for a ship ai segment when the ship runs away… so it turns away then just goes forwards from there till told to stop.

also any ideas on how to make the ship circle around its target a set distance? so basically it would sit and circle the target firing its weapons till told to stop.

you could lerp the rotation