Duration of stay varies. Some students may have work authorization . Others may be eligible for optional practical training , a work authorization for one year after graduation in their field of study. Whether applying for a temporary or permanent visa, allow plenty of time. After all, you're dealing with federal agencies.
Foreign nationals can obtain green cards through employment.
Getting such permanent residency is usually a long process. For some, it may take five or more years. In most cases, the employer sponsors the foreign national by offering a permanent job. That doesn't mean employment for life. For immigration purposes, permanent means a job that lasts as long as both the employer and employee want it to last.