You can control what information is shown on the timeline below the map by double-tapping it:
Choose from the displayed options:
The user guide within the app shows what information (e.g. Nautical, Astronomical Twilight, Golden Hour, Sun Transit etc.) is shown with each option, but they're hopefully fairly self-explanatory.
Once you select a new option, the timeline displays the corresponding entries:
Note that the display options for Night Mode can be selected independently: