A listing stays in search for 30 days. Once every 3 days you can bump it to the top for free.
A listing stays in search for 30 days. After that it expires and leaves the search; you still find it in My listings.
Bump moves a listing back to the top of the default order, as if it had just been posted. It’s free once every 3 days. Use it when the listing is still current, for example after lowering the price.