The LUX Getting Started guide has instructions for deploying the LUX snippet. This explains how to put lux.js in your pages in order to collect LUX data from your real traffic.
Those instructions say to put the LUX snippet as early in the page as possible, i.e., at the top of the HEAD element. Some customers use tag managers and have asked if the LUX snippet can be deployed that way.
Following the guidance in the LUX Getting Started guide solves these problems. Including the LUX snippet at the top of the page allows it to collect CPU Time data from the beginning, and means that even users that leave the page before onload are tracked. Finally, putting the LUX snippet at the top of HEAD gets the LUX API declared immediately so it can be used throughout the page even while lux.js is being loaded asynchronously.