The frequency on inventory syncs depends on your ecommerce store.
- Shopify and BigCommerce inventory updates are in 'real time' - if you change the inventory in Shopify/BigCommerce, Trade Runner receives notification of the change and then updates Trade Me.
- Magento inventory is updated every 20 minutes.
- WooCommerce inventory is updated every 24 hours (overnight with the full product sync).
Stock is decremented when an order is processed which is covered in this article - http://traderunnersupport.omnivore.com.au/support/solutions/articles/17000055416-inventory-and-orders
More details are available in the Syncing FAQs