Right. The goal is to achive the maximum separation that your flexibility allows. Thus, you need to keep the shoulders closed until the hips have opened as far as they can. Good mechanics and timing are required to do this.
Also, I wouldn't say the belt buckle is facing home plate at foot plant but right after foot plant. At foot plant, the hips should have opened only enough to allow the front leg/foot too open into foot plant. The remainder of hip rotation occurs after the front foot has planted and the front leg has firmed up and braced.