Parashas Bo · Shemos 12:15 · TT note 7
Torah Temimah on Shemos 12:15, note 7 (on אַךְ) points to Pesachim 5a.
Sefaria — Exodus 12:15
Sefaria — Torah Temimah on Exodus 12:15
Sefaria — Pesachim 5a
E-Daf — Pesachim 5a
English: And say [perhaps only] from the morning? “Ach” divides [the day — part permitted, part forbidden].
Division of the fourteenth via the word אַךְ.
Not the whole fourteenth is for biur from dawn; אַךְ splits the day so that biur begins at a midpoint (sixth hour), not only at morning.