When it comes to audience retention, it is generally measured as a percentage- that is, what percentage of your audience members return to your service or platform within a certain period of time. This can be used to measure the effectiveness of your content or campaigns and can help you decide when to make certain changes or updates. However, this doesn't mean that time isn't important too- it's just that time isn't usually the sole focus when it comes to audience retention. That said, it is important to know how much time it takes for users to return, so that you know how often you should be pushing out new content or campaigns for the best results.