Congratulations on pursuing your career. As former CTS Specislist for Job Corps, each program is different. Completion time is totally based on you. Trade specific trainings tend to take 6-9 months but if you're also pursuing your high school diploma while in Job Corps then that could end up being a year or so.
Furthermore I would definitely encourage your to continue with Job Corps' advanced culinary program one you've completed the basics. Some advanced programs may take another 9 months to 1 year. Remember once your done with training the real work begins. It will be hard but fun also rewarding to see people enjoying your meals. Good Luck!