In general, the majority of jobs submitted to job boards through SmartRecruiters are 30-day listings, especially for the free job aggregator boards. After this period ends, boards and aggregators will drop the job from their feed unless you republish the job.
Be careful not to repost/republish your your jobs to the free aggregators too frequently. Aggregators may blacklist your jobs or bury them farther down the results if you republish jobs before the listing expires.
Depending on the on the type of package you purchased through SmartRecruiters, your jobs' lifetime on a paid board may vary.