Because Marketplace Connect sits inside Shopify, there's no data migration to a separate multi-channel platform required, which can save days or even weeks of setup time.
Installation and connecting your chosen marketplace can take minutes, depending on the marketplace, and account requirements.
Setup time is dependent on how many different configurations you have for your products but all changes can be done in bulk. Even for the most complicated configurations, it's rare that merchants aren't selling on the same day.
For further assistance, please reach out to marketplace-connect@shopify.com