"...in the night odwołuje się do konkretnej nocy a at night do nocy ogólnie..."
What are you trying to say?
She left before night. She left during the night. She left at night. She left by night. It was night when she left. It was the night when she left. As night fell, she left. As the night fell, she left.
Which of those above are "konkrente" and which "ogolne?"