Why does a long backfill take a while?

Because Shopify limits how fast any app may read a store, and a long history can hold hundreds of thousands of orders. The backfill is nouz's first import of your whole order history. It runs in pieces and waits whenever Shopify asks it to.

nouz uses Shopify's bulk operations for it. That is Shopify's way of handing over a big export. Shopify prepares the file on its side, and nouz reads it once it is ready. While Shopify prepares it, the import screen says “Shopify is preparing your data”. Then you know the wait is on Shopify's side.

The import goes in order. First your products, then your orders with their payments and refunds, then your shipments. Last, nouz builds your daily numbers from all of it.

A store with a few thousand orders is usually done in minutes. One with hundreds of thousands can take hours. You do not need to watch it, and you can use the app meanwhile. Each piece is saved as it arrives. If something interrupts the import, it goes on where it stopped instead of starting over.

Later syncs are much faster, because they only fetch what changed. To see how far the import is, open Settings, then Integrations, and look at Order history.