TT #54 · Parashas Va’eschanan · Passuk 6:7
…and when you lie down and when you rise up.
Torah Temimah points to the classic derivation of the times for evening and morning Shema from “uve-shokhbekha uve-kumecha” (Berachos 2a).
English: From when may one recite the evening Shema? … The Tanna is basing himself on the verse, as it is written “when you lie down and when you rise up.” What is meant by “when you lie down and when you rise up”? At the time when people lie down and at the time when people rise.
Diyuk of “uve-shokhbekha uve-kumecha” as the times of ordinary human sleep and rising.
The evening and morning Shema are recited at the times when people normally lie down and rise; the verse itself defines the windows.