If you mean the time of the day, then you can switch to the main watch face anytime (even during an activity in progress). I am not familiar with Lily 2, but on most other models, you do it by pressing the Back button. If the button is used for marking laps, you can assign a hot-key for the same functionality (if you do not know how to set up a hot key, consult the user manual for your watch, but on my watch it is in the settings menu » System » Hotkeys).
Another possibility is adding a data screen with the current day time, and scrolling to it during the activity. Most of activities usually already have such screen in the default configuration (at least on my watches).
