After I build my catalog, how long does the product takes to appear on my online store?

If you add products through Admin panel, they will reflect immediately on your store as soon as you click the "Save" button.
But in case, you are have uploaded in bulk through CSV format files, it will take some time depending on the number of products.

Refer to our helpcenterlinks below to know more:
Adding and updating products in bulk-
https://help.storehippo.com/topic/adding-and-updating-products-in-bulk

Adding a Single Product-
https://help.storehippo.com/topic/adding-a-single-product