Hermit is designed in such a way that it and its package manifests are always on the latest version. To that end, Hermit will check for and upgrade to new releases of itself once every 24 hours, and will sync to the latest package definitions every 24 hours. If you notice a pause when using Hermit, this is often the cause.
You can read more about the implications of this on package maintenance in the packaging introduction.
In addition, some packages may define channels which allow packages to be kept up to date automatically with upstream releases. Channels specify their own update frequency which Hermit will use to periodically check for updates. If the ETag for the package has changed, Hermit will download and upgrade the package.