Parashas Vayikra · Aliyah 1 · Passuk 4
Chabad.org — English translation + Rashi
Torah Temima points to Megillah 20b.
E-Daf / Tsurras Hadaf (size=3 where available)
PDF of the daf / source
English: The entire day is valid for s’michah, because the verse places “and he shall lean” next to “and he shall slaughter”; just as slaughter is valid all day, so is leaning valid all day.
Establishment of the time frame of the mitzvah of semichah — it must be performed by day and in proximity to the slaughter.
One may perform the leaning at any time during the day, giving flexibility while still linking the personal act closely to the subsequent slaughter.