Random Cache Expiry

Question

I've been experimenting with random cache expiry times to avoid situations where an individual request forces multiple things to update at once. For example, a web page might include five different components. If each is set to time out in 30 minutes, the user will have a long wait time every 30 minutes. So instead, you set them all to a random time between 15 and 45 minutes to make it likely at most only one component will reload for any given page load.

I'm trying to find any research or guidelines on this topic, e.g. optimal variance parameters. I do recall seeing one article about how Google (?) uses this technique, but can't locate it, and there doesn't seem to be much written about the topic.