Yes, your job pack will expire depending on the job pack you purchased.
1 - 5 job pack will expire 30 days from the date of purchase.
6 - 9 job pack will expire 60 days from the date of purchase.
10+ job pack will expire 90 days from the date of purchase.
Any remaining credits from your package will no longer be available after expiration. You can also see when your credits expire under your employer account by clicking on "manage jobs (checklist icon)" then "purchase history (dollar sign/folded page icon)".