«ثُمَّ أَتِمُّوا الصِّيَامَ إِلَى اللَّيْلِ»
“Then complete the fast until night.”
Night marks the end of the daytime fasting period. It does not mean that night itself becomes an additional period of the same required abstention.
Recognizing the endpoint identifies when the relevant temporal obligation ceases. The requirement of daytime fasting is not extended beyond sunset merely because the expression uses ila.