We use the time interval swap method. This works well for template based platform sites like Shopify where you don’t have much control over the backend / server.
This means that we swap themes on the server side, rather than the client side (like if you were doing split traffic method), so there is no performance lag and no rendering lag during page load.
For product tests, Shopify requires the produce price to be stored in the store database, so it’s not possible to show 2 different prices to 2 different visitors (unless you duplicate the product).
When you start an A/B test, Theme Scientist will swap your versions at the interval you selected (every 30 minutes up to every day).