Parashas Vayikra · Aliyah 1 · Passuk 4
Chabad.org — English translation + Rashi
Torah Temima points to Megillah 20b (verified; semicha is valid all day by juxtaposition with slaughter).
E-Daf.com — Tsurras Hadaf (size=3)
HebrewBooks / Shas PDF of the daf
English: “And he shall lean” — the entire day is valid for leaning, as it is written “and he shall lean,” and next to it “and he shall slaughter”; just as slaughter is valid the entire day, so leaning is valid the entire day.
Custom (juxtaposition / semuchin) — semicha is learned to be a daytime mitzvah valid all day from its placement next to slaughter.
Semicha may be performed at any time during the day (dawn to dusk), parallel to the time frame of slaughter.