You can finish your study whenever you want (whether all participants complete their task or not, it depends on you). When you finish the study, you will still be able to access this study dashboard, but no more participants will be allowed to participate. You can restart your study at any time. The test URL will not change, and you can invite more users to test your items.
NOTE: Once you order RealEye panelists, you won't be able to change study/item settings, revert the study to draft, or finish the study until all results are collected.