This is a good lesson on being a good citizen of the Internet.

It's easy to just curl a feed every second, but should you? (Of course not)

Take it as a challenge to make your reader as fancy as possible, use every trick in the book to optimise how it fetches content. Analyse the patterns of releasing new content per feed and adjust the fetch frequency based on that.

And if you're building a reader for distribution, don't let the user set a refresh interval that doesn't make sense.