The tutorial discusses optimizing build times on CircleCI by splitting tests based on timing data, specifically for a React.js application using jest-junit. It explains how CircleCI divides tests across multiple nodes using parallelism, allowing each container to run a portion of the tests simultaneously. The process involves configuring Jest to generate JUnit test reports, which CircleCI uses to analyze and distribute test timings evenly. By adjusting the package.json file and utilizing CircleCI's capabilities, developers can achieve more efficient test runs both locally and in CI environments. The tutorial provides step-by-step instructions on setting up this configuration, emphasizing the importance of experimenting with the number of nodes to find the optimal configuration for each test suite.