UAS Daylight Operation Only
This URL and others provide the official sunrise and sunset times for any location.
§ 107.29 Daylight operation.
No person may operate a small unmanned aircraft system except between the hours of official sunrise and sunset.
Sunrise and sunse as used by the FAA do not mean when you can barely see. That is twilight. Sunrise and sunset are specific times per the URL above. At or after sunrise, the sun is visible. The same with sunset, if you can't see the sun any more, it is past sunset.