To change the handling time for your Amazon listings, you'll want to start by navigating to your Amazon Listings Tab.
Click on the listing you would like to edit and scroll down to the "Handling Time" field and enter a handling time of your choosing. Once you have done this, click on the "Save & Publish" button to publish your changes. If you need to change your handling time in bulk, you will want to do so using Amazon Presets.
NOTE* If you do not have a handling time entered in Sellbrite, the default handling time set up in your Amazon account will be used.