Heart beat not working?

I’m have the HeartBeatTimer enabled per: JavaScript Tracking Client: Integrate - Matomo Analytics (formerly Piwik Analytics) - Developer Docs - v3

However, the users are still listed as having spent 0s on the page. Is there additional configuration that is needed?

This may cause by the user has reach and interact less than the interval has set (15sec ? 30 seconds?)

https://developer.matomo.org/guides/tracking-javascript-guide