Impression Interval is used to set the minimal interval between fullscreen ads, or to set banner refresh time for a specific placement. E.g. a fullscreen ad is shown after completing a level in a game, and it’s needed to arrange the ads in a way that the users who complete levels faster don’t watch ads more often. In this case the limit can be set to 1 minute. It means that if some users complete some levels in less than a minute — the ads will not be shown in those particular cases. And if such users take 2 minutes to complete a level — only one ad will be shown afterwards, in accordance with the game logic.
Moreover, Appodeal updates the banner ads automatically by default, depending on general settings based on your analytics. However, with Impression Interval you can set the timing of banner refresh manually — it will go in effect for this particular placement. Take note that auto cache is enabled by default and can be disabled via source code — but we do not recommend doing that for banners.