Siman 431
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א בִּתְחִלַּת לֵיל י"ד בְּנִיסָן בּוֹדְקִים אֶת הֶחָמֵץ לְאוֹר הַנֵּר, בַּחֹרִין וּבַסְדָקִין, בְּכָל הַמְּקוֹמוֹת שֶׁדֶּרֶךְ לְהַכְנִיס שָׁם חָמֵץ.
1 The Time for the Search of Chametz, 2 Seifim: At the beginning of the night of the 14th of Nisan, we search for chametz by the light of a candle in holes and cracks in every place that it would be usual to have brought chametz.
ב יִזָּהֵר כָּל אָדָם שֶׁלֹּא יַתְחִיל בְּשׁוּם מְלָאכָה וְלֹא יֹאכַל, עַד שֶׁיִּבְדֹּק. וַאֲפִלּוּ אִם יֵשׁ לוֹ עֵת קָבוּעַ לִלְמֹד, לֹא יִלְמֹד עַד שֶׁיִּבְדֹּק; וְאִם הִתְחִיל לִלְמֹד מִבְּעוֹד יוֹם, אֵין צָרִיךְ לְהַפְסִיק. וְיֵשׁ אוֹמְרִים שֶׁצָּרִיךְ לְהַפְסִיק, וְכֵן נִרְאֶה לִי עִקָּר.
2 Every person must be careful not to start any work or to eat until they have searched. Even if they have a fixed time to study, they should not study until they have searched. If they started learning while it was still day, they don't have to stop ( and some say they do have to stop, which seems correct to me)