Siman 238
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 צָרִיךְ לִזָּהֵר בְּלִמּוּד הַלַּיְלָה יוֹתֵר מִבְּשֶׁל יוֹם, וְהַמְבַטְּלוֹ, עָנְשׁוֹ מְרֻבֶּה.
1 Establishing fixed times for Torah study at night. This chapter contains two paragraphs: One must be more careful with nighttime Torah study than with daytime study, and one who neglects it receives a greater punishment.
ב אִם יֵשׁ לוֹ חֹק קָבוּעַ לִלְמֹד כָּךְ וְכָךְ לְיוֹם וְהָיָה טָרוּד בַּיּוֹם וְלֹא הִשְׁלִימוֹ, יַשְׁלִימֶנּוּ בַּלַּיְלָה מִיָּד.
2 If a person has a fixed daily portion of study and was preoccupied during the day and did not complete it, he should make it up immediately at night.