Why does “ila al-layl” not simply add night to the duration of fasting?

Particles of Meaning: Aw, Hatta, Ila, Ala, Fi and Ba

• Night is a distinct limit after the daytime fasting period
• Because ila includes the following period within the preceding ruling
• Because night and day form one continuous period that must both be included
• Because the fast must continue into a portion of the night