Verse 4 mentioned the afternoon. Why does our verse mention night?
Radak (4): These are times of calamities - "mi'Dever ba'Ofel mi'Ketev Yashud Tzaharayim" (Tehilim 91:6). They attack at difficult times for [Yisrael].
Malbim (4): She (Tziyon's residents) is pampered and sleeps in her house in the afternoon and does not go outside due to the sun. It is easy to ascend there without resistance. The enemy did not. When it was late in the day, they said, now there is shade, and she can go out! Rather, we will attack at night, when she sleeps. The metaphor calls Anshei Yerushalayim a pampered woman who is too delicate to leave her house at these times.
Why did they want to destroy the palaces?
Radak: Jews thought to be protected there.
