Public libraries can support a wide area small population rural community, or a big city environment such as Los Angeles or Chicago. A commercial library typically supports the needs of their corporate host. Many governments at all levels are growing into the need for an archivist to manage their historical documents. There are other terms of time commitment. Some jobs will provide the successful applicant with short term commitment with the possibility of a longer term contract.
Some jobs are fulltime for as long as a project lasts.
The job may be measured in months. Nice work if you can get it. And, there are some employment agencies that specialize in filling temporary labor needs or more long term jobs to librarians. Experience Level - The ad will typically make it known what level of experience is needed. The classic levels are entry level, professional level of a function, team leader, department head, and director.