Stories will be cached as soon as someone goes to your storefront and prompts the app to retrieve your current stories from Instagram. From that moment, your stories will stay cached for 20 minutes. This feature helps the widget serve up your content faster and to more people while also reducing the number of API calls each store makes per day. After 20 minutes, your cached stories will expire, making room to cache any new stories that may of been uploaded in that 20 minute window.
To clear the story cache, you can change any setting in the app. We recommend you don't enable the app till you have your settings configured to your liking. This helps keep your page calls to Facebook under the in place API limits.