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Roughly speaking:
Nighttime ends at Astronomical Twilight, (when light is first detectable in the sky and begins to obscure the stars).
This is followed by Nautical Twilight, (when there is sufficient light to see and be seen at sea).
This is followed by Civil Twilight, (when street lights are switched off).
This is followed by Sunrise, (when the sun rises above the horizon).

Sunrise and sunset times in London https://www.timeanddate.com/sun/uk/london

As usual tradition goes against the Word of Elohiym which clearly states that the day begins at dawn; daybreak if you like :)