Can I run the import every day to add new items from Amazon?
Unfortunately this is not what the import feature in WP-Lister for Amazon is designed for. It is designed for migrating all items from Amazon to WooCommerce once – and let WP-Lister take care of managing and syncing items from that point on.
WP-Lister is mainly a listing application: It's purpose is to list items from WordPress, hence the name. If you need to add new products on Amazon directly and have those changes reflect in WordPress automatically, then you should look into alternative options like sync services hosted on third party servers or embedding amazon products directly into your website.
If you are currently using an inventory update system which pushes updates to Amazon directly, you need to find another system to push these updates to WooCommerce instead. See the related article about CSV import plugins below.
Why can't WP-Lister just stay in sync with changes I make directly in Seller Central?
Because Amazon doesn't notify WP-Lister when there was a change on their side. As a WordPress plugin, WP-Lister is "aware" of anything that changes within WordPress, for example editing a product or placing an order. But to learn about changes on Amazon, it has to pull this information from Amazon, either via their API or by requesting and downloading reports.
While the API works well enough for fetching the latest orders, it doesn't tell which products were most recently edited. That would require processing a full inventory report, which takes considerable time to request and process so this can't work as a "real time" update. Additionally, processing large reports and importing new products is a process that requires too many resources to run sufficiently as a background task. A WordPress plugin is rather limited when it comes to memory and execution time - while a service that runs on a third party server doesn't have this kind of limitation.
That's why WP-Lister for Amazon only allows you to automatically request and process a Merchant Inventory Report once a day - by enabling the Process daily inventory report option on the advanced settings page. However, if you think you need to do this more often, you can set up a separate external cron job and point it to the URL
http://example.com/wp-admin/admin-ajax.php?action=wpla_request_inventory_report. (replace "example.com" with your domain.)
We do not recommend to do this, so use it on your own risk. Please note that you have to keep the Process daily inventory report option enabled, otherwise WP-Lister would not automatically process your report.