You can configure NitroSell eCommerce to select all products created in the past X Days.
For example, to mark any item created in the last 60 days as being a New Product on the WebStore, perform the following steps :
In NSc Sync Configuration, under Advanced, select Field Mappings.
Under Item, right-click product_newproduct.
Select Properties, then click Advanced.
Change the Field Source for product_newproduct to:
CASE WHEN DATECREATED > GETDATE()-60 THEN 1 ELSE 0 END
Click Validate, then click OK.
To check which products are new on your webstore see: