It really depends on how you view the admissions process. The upper tier, highly competitive schools will release their essays sometime this Summer and the applications in late Summer or early Fall. From there, the interview and admit decisions can take anywhere from a couple of weeks to a few months. Each school is different. If you are interested in specific schools, visit their admissions sites now and you'll get a good approximation of their timelines for next year.
That said, the admissions process really takes much longer than that. Aside from the obvious items like seeking out responsibility and succeeding professionally, you need to study for and take the GMAT, create or update your resume, think about potential recommenders, and seek to address any weak spots in your profile. If you lack leadership experience, you may need to look outside of work to obtain that experience via charity work or other extracurricular activities. If you're GPA needs help, you may want to take a couple of classes.