It was dark by the time the police arrived.
I do alot of walking in the area and the parks kick us out (close) after sunset. Generally on December 20th, I have to be out of the park by 6 pm. It still stays light after the sun sets. Civil twilight lasts about 15 minutes in San Antonio.
I always plan my walks according to the sun. We do have police patrolling the parking lots and trails on ATVs. You can be there during civil twilight because it is still light, but if they catch you coming to your car afterwards, they will often say something.
Generally it is dark at the end of civil twilight.
It was not dark when Lina was last seen. Shadows get longer, but it was not dark.
Note: The light issue is a big deal in the summer for me, because I time my walks so that the walk ends at the end of civil twilight. (Long story...LOL..but it has to do with Texas heat!..I gotta start being careful around the end of July..days suddenly get shorter..LOL...I also know the exact time that I need to use a flashlight in yard and I've got lanterns and the whole works. Our watering time is 7 pm - 11 pm. )
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Note: Civil twilight is shorter near the equator. It lasts about 15 minutes in Texas.
Civil twilight is the period when enough natural light remains that artificial light is not needed.
Lawmakers have enshrined the concept of civil twilight. Such statutes typically use a fixed period after sunset or before sunrise (most commonly 20–30 minutes), rather than how many degrees the sun is below the horizon. Examples include the following periods: when drivers of automobiles must turn on their headlights (called
lighting-up time in the UK); when hunting is restricted; when the crime of
burglary is to be treated as nighttime burglary, which carries stiffer penalties in some jurisdictions.
Twilight - Wikipedia