"Sunrise" or "Civil Twighlight" when calculating light start time for light dep?

Good Day

First time caller, long time listener.

We have harvested indoor for years, but this is the first time we are moving to outdoors, starting with a spring light dep. We are very excited, but also trying to do our due diligence.

It seems that the method we will probably use is: to pull the blackout fabric after 12 hours of natural light, then uncover them an hour after it is dark. This will allow them 12 hours of light and 12 hours of dark, but also allow them to be uncovered with natural airflow during the natural dark time.

My question is more about the LIGHT TIME.

Do we calculate the start of the 12 hour LIGHT from Sunrise or Civil Twilight?

Civil Twilight is 26-30 minutes before Sunrise for the dates we are aiming for.

So, does that 30 minutes of Civil Twilight count as light?

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For example:

On March 21st the Civil Twilight is 6:45 am, and the Sunrise is at 7:12 am. Should we ideally in a perfect world cover the hoop house at 6:45 pm or 7:12 pm that night?

doesn't really matter in my experience. i would miss the time by about 15-20 minutes a day on average. flowering still went off without a hitch.

I use local sun rise times

come daylight saving if used locally?

I like to split them 30 minutes each way

they settle in fast and adept quick

they bitch and cry come door slamming time ...lol

good luck