Siman 652
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 מִצְוַת לוּלָב בַּיּוֹם וְלֹא בַּלַּיְלָה; וְכָל הַיּוֹם כָּשֵׁר לִנְטִילַת לוּלָב, שֶׁאִם לֹא נָטַל שַׁחֲרִית, יִטְּלֶנּוּ אַחַר כָּךְ. וּמִכָּל מָקוֹם זְרִיזִים מַקְדִּימִים לְמִצְוֹת וְנוֹטְלִים אוֹתוֹ בַּבֹּקֶר; וּזְמַנּוֹ הוּא מִשֶּׁתָּנֵץ הַחַמָּה, וְעִקַּר מִצְוָתוֹ בִּשְׁעַת הַהַלֵּל, וְאִם צָרִיךְ לְהַשְׁכִּים לָצֵאת לַדֶּרֶךְ, נוֹטְלוֹ מִשֶּׁעָלָה עַמּוּד הַשַּׁחַר. הַגָּה: וְהַמְדַקְדֵּק יֶאֱחֹז הַלּוּלָב בְּיָדוֹ כְּשֶׁנִּכְנָס מִבֵּיתוֹ לְבֵית הַכְּנֶסֶת, גַּם בִּשְׁעַת הַתְּפִלָּה, וְכֵן יַחֲזִירוֹ לְבֵיתוֹ, כְּדֵי לְחַבֵּב הַמִּצְוֹת (טוּר).
1 The Time For The Taking Of The Lulav, 2 Seifim: The mitzvah of lulav is during the day and not at night. The whole day is fitting for taking the lulav; if one did not take it in the morning, they can take it later. In any event, those who are prompt do mitzvahs early and take it in the morning. Its time starts at sunrise. The core time to do the mitzvah is during Hallel. If somebody needs to wake up early to travel, they should take it at dawn. Rema: One who is precise should hold the lulav in their hand when entering the house or the synagogue, even during prayers, and also when returning home, so as to be affectionate towards the mitzvahs (Tur).
ב אָסוּר לֶאֱכֹל קֹדֶם שֶׁיִּטְּלֶנּוּ; וְאִם שָׁכַח וְאָכַל וְנִזְכַּר עַל שֻׁלְחָנוֹ בַּיּוֹם הָרִאשׁוֹן, שֶׁהוּא מִן הַתּוֹרָה, יַפְסִיק, אֲפִלּוּ יֵשׁ שְׁהוּת בַּיּוֹם לִטְּלוֹ אַחַר שֶׁיֹּאכַל; וּמִיּוֹם רִאשׁוֹן וָאֵילָךְ, אִם יֵשׁ שְׁהוּת בַּיּוֹם לֹא יַפְסִיק; וְאִם לָאו, יַפְסִיק. הַגָּה: וְאִם הִתְחִיל לֶאֱכֹל יוֹתֵר מֵחֲצִי שָׁעָה קֹדֶם שֶׁהִגִּיעַ זְמַן חִיּוּבוֹ, אֲפִלּוּ בְּיוֹם רִאשׁוֹן אֵינוֹ צָרִיךְ לְהַפְסִיק בִּדְאִכָּא שְׁהוּת בַּיּוֹם (רַ"ן פ' לוּלָב הַגָּזוּל).
2 It is forbidden to eat before taking it. If one forgot and ate and remembered while eating, if it is the first day when it is a Torah obligation, they should stop [and take the lulav] even if there will be sufficient time in the day to shake it after eating. On subsequent days, if there will be time [after eating] they need not stop [eating]. Otherwise, they should stop. Rema: If one started eating more than a half-hour before the onset of the obligation, even on the first day, one need not stop [eating] as long as there will be time during the day (Ra"n ch. "Lulav haGazul").