Zentail sends feeds to Amazon every 15 minutes on the hour. This means Zentail sends updates at :00, :15, :30, and :45.

Depending on catalog size and feed type (product data, order data, inventory data, pricing data), an edit in Zentail made just before the 15 minute interval may not be included in the most immediate feed because Zentail needs to build these feed in advance of the interval time.  Amazon can take 1 to 5 minutes to update once the feed is received.