While importing less than a thousand products to your store can be relatively fast, syncing large catalogues with SKU counts in the thousands can take quite a while. This is due to the limitations of the Shopify API and the number of requests Partbot is permitted to make per second.
Importing thousands of products can take several hours, but rest assured the process will complete eventually; once your initial import is complete future updates are very fast, if not real-time.
We are working on improving the import process for large catalogues for Shopify stores - stay tuned for future updates!