That is because Allah causes the night to enter the day and causes the day to enter the night and because Allah is Hearing and Seeing.
The Saheeh International Quran Translation
ذَٰلِكَ بِأَنَّ ٱللَّهَ يُولِجُ ٱلَّيْلَ فِى ٱلنَّهَارِ وَيُولِجُ ٱلنَّهَارَ فِى ٱلَّيْلِ وَأَنَّ ٱللَّهَ سَمِيعٌۢ بَصِيرٌThat is because Allah causes the night to enter the day and causes the day to enter the night and because Allah is Hearing and Seeing.