Incremental builds

Hey Netlify Community! I just followed the guide to set up incremental builds with gatsby and netlify: https://www.netlify.com/blog/2019/01/17/how-to-scale-massive-react-static-sites-with-incremental-builds/

Everything builds as it should but when I checked the build time it was the same as before. Here is a link to my apps page https://app.netlify.com/sites/weroast/deploys
Are the builds supposed to be significantly faster with the plugin? If so did I miss something in my configuration? Here is a link to my toml https://github.com/L-Town-FC/we-roast/blob/dev/netlify.toml

Any thoughts?