Whether you purchase a single job posting or purchase ten at a time, you do not have to use them immediately. Your purchase does not expire. So you can post a job whenever you have an opening, and keep your remaining job posts in reserve until you’re ready to hire again.
Once published, each job posting is displayed for 30 days. So you can use your remaining purchased posts to list new jobs, or to extend a current opening if you haven’t yet filled it.