If for whatever reason Life Cycle can't log all your activities, because your phone needs to be turned off, or you can't always bring it with you, or something else - then you can add activities manually, afterwards.
Just press the Plus sign at the top left corner. From there, you can input any activity through any time, and Life Cycle's donut will update accordingly. Eventually, the app will learn your manual log habits and make this process easier for you, by predicting what you want to log.
More specifically, if you want to add an activity within an activity (if you worked from home, for example) click on the slice where you want to add an activity, and then on the Plus sign that appears below.