Siman 443
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 חָמֵץ מִו' שָׁעוֹת וּלְמַעְלָה בְּיוֹם י"ד, אָסוּר בַּהֲנָאָה, אֲפִלּוּ חֲמֵצוֹ שֶׁל עַכּוּ"ם אָסוּר לֵיהָנוֹת מִמֶּנּוּ (טוּר סִימָן ת"ן וריב"ש סִימָן ת'), וַאֲסָרוּהוּ חֲכָמִים שְׁתֵּי שָׁעוֹת קֹדֶם דְּהַיְנוּ מִתְּחִלַּת שָׁעָה חֲמִישִׁית, וּמִיהוּ כָּל שָׁעָה חֲמִישִׁית מֻתָּר בַּהֲנָאָה, וְרַשַּׁאי לְמָכְרוֹ לְעַכּוּ"ם, אֲפִלּוּ הַרְבֵּה בְּיַחַד שֶׁוַּדַּאי לֹא יֹאכְלֶנּוּ קֹדֶם פֶּסַח; וְיָכוֹל לְהַאֲכִילוֹ לִבְהֵמָה חָיָה וְעוֹף, וּבִלְבַד שֶׁיַּעֲמֹד עֲלֵיהֶם לִרְאוֹת שֶׁלֹּא יַצְנִיעוֹ מִמֶּנּוּ, וִיבַעֵר מָה שֶּׁשִּׁיְּרוּ מִמֶּנּוּ, וּמִתְּחִלַּת שָׁעָה שִׁשִּׁית וּלְמַעְלָה, אֲסָרוּהוּ גַּם בַּהֲנָאָה. הַגָּה: וּבִשְׁנַת הָעִבּוּר שֶׁהַיּוֹם אָרֹךְ, אֵלּוּ הָאַרְבַּע שָׁעוֹת לְפִי עִנְיַן הַיּוֹם וּמֻתָּר לֶאֱכֹל חָמֵץ עַד שְׁלִישׁ הַיּוֹם (רַמְבַּ"ם בְּפֵרוּשׁ הַמִּשְׁנָה רֵישׁ בְּרָכוֹת וּמַהֲרִי"ו), וְיֵשׁ אוֹמְרִים עַד ב' שָׁעוֹת קֹדֶם חֲצוֹת (תְּרוּמַת הַדֶּשֶׁן סִימָן קכ"א).
1 Status of chametz on Pesach Eve after sixth. Contain 3 sections: Chametz from the sixth hour and on on the fourteenth is prohibited to benefit from (even chametz of gentiles is prohibited to benefit from) (Tur and Rivash) and the Sages proscribed two hours previously, for from the start of the fifth hour and within it is permitted to benefit and permissable to sell it to gentiles even many at once, because we certainly do not eat it before Passover, though you can feed it to wild animals and birds, and only if you watch over them lest they be deterred from it and they eat what they have measured. And from the start of the sixth hour and on they proscribed it even in benefit. Rema: And in a leap year when the day is long these are four hours according to the nature of the day, and it is permitted to eat chametz until a third of the way through the day. And some say until two hours before noon.
ב יִשְׂרָאֵל שֶׁהָיָה בְּיָדוֹ חֲמֵצוֹ שֶׁל יִשְׂרָאֵל אַחֵר בְּפִקָּדוֹן, יְעַכְּבֶנּוּ עַד שָׁעָה חֲמִישִׁית, וְאִם לֹא בָּאוּ בְּעָלָיו יִמְכְּרֶנּוּ לְעַכּוּ"ם; וְאִם לֹא מְכָרוֹ חַיָּב לְבַעֲרוֹ בִּזְמַן אִסוּרוֹ, אֲפִלּוּ אִם אֵינוֹ חַיָּב בְּאַחֲרָיוּתוֹ.
2 An Israelite which has the chametz of another Israelite in hand as collateral -- we delay until the fifth hour, and if its master doesn't come we sell it to gentiles, and if he does not sell it he is obligated to burn it in its time of proscription, even if if he wasn't obligated it its responsibility.
ג אִם קָנוּ שׁוּם דָּבָר בְּחָמֵץ אַחַר שֵׁשׁ שָׁעוֹת, מֻתָּר מִפְּנֵי שֶׁחָמֵץ אֵינוֹ תּוֹפֵס דָמָיו.
3 If he exchanges anything for the chametz after the sixth hour, it is permitted, because chametz does not take effect on its money.