Exodus 23:18

Sons of Israel My people, while there is leaven in your houses you may not immolate the bloody sacrifice of My Pascha; nor shall the fat of the sacrifice of My Pascha remain without the altar until morning, nor of the flesh that you eat in the evening.

THOU SHALT NOT OFFER THE BLOOD OF MY SACRIFICE WITH LEAVENED BREAD. “You shall not slaughter the Passover-offering on the fourteenth day of Nisan before you have removed the leavened bread [from your possession].” This is Rashi’s language.
Do not interpret the meaning of this statement of Rashi to refer to the removal of unleavened bread, [and that the verse tells us] that this must take place before the time of slaughtering the Passover-offering, just as is mentioned in the first chapter of Tractate Pesachim: (further 34:25), which means: “do not slaughter the Paschal-lamb while the leavened bread is still there.” And since the time for the slaughtering of the Paschal-lamb begins after the sixth hour, we therefore deduce that unleavened bread is forbidden from that time on. When the Gemara further asked: “Perhaps the Torah meant a separate time for each individual, [so that if he slaughtered it on the ninth hour of the day, he would not be in violation of the law against keeping unleavened bread till such time]? To this the answer is given: “The Merciful One has declared a time for the slaughtering of the Passover-offering [for all alike, and He did not distinguish between one person and another]. — Ramban is now writing that Rashi’s explanation was not prompted by this text of the Gemara, for reasons explained further on. “The Merciful One has declared a time for the slaughtering of the Passover-offering for all alike” — for this interpretation is not the real point of the verse in accordance with the final decision of the law mentioned there. For there is no prohibition commandment, thus one who failed to remove it from his possession after the sixth hour of that day, has thereby violated a positive commandment. But there is no negative commandment to cover this matter. Hence the verse before us which is a negative commandment cannot be establishing the time for the removal of unleavened bread, since that is covered only by a positive commandment. This is the intention of Ramban’s words. according to the law of the Torah requiring the removal of unleavened bread on the day before Passover, not even is there a prohibition against eating it [but the violation of a positive commandment]. commandment of the Torah covering it, but one who eats it violates thereby a positive commandment, since he had failed to destroy the unleavened bread beforehand. See, however, “the Commandments,” Vol. II, p. 196, where Rambam differs on this point and counts a specific negative commandment, wherein we are forbidden to eat unleavened bread after the middle of the fourteenth of Nisan. But the subject of the verse as established according to the final decision of the law, is an admonition against slaughtering the Passover-offering with leavened bread, meaning that none of the company who have been counted to eat of this Passover-offering, may have leavened bread remaining in their possession at the time it is slaughtered. And so Rashi explained it in the section of Ki Thisa. Now the verse should have read, “Thou shalt not slaughter with unleavened bread My sacrifice” [omitting the word: dam — blood], for the blood is not “slaughtered.” But in the opinion of our Rabbis this comes to include the sprinkling, so that the priest who sprinkles the blood of the offering is also forbidden to have leavened bread in his possession. The verse thus states: “Do not slaughter the Passover-offering with unleavened bread, and neither [sprinkle] the blood of My sacrifice,” That is, and neither let the blood of My sacrifice be with unleavened bread. It is an elliptical verse.

לא תזבח על חמץ, the elimination of leavened products must take place before it is legally possible to slaughter the Passover, i.e. not later than the 6th hour, before noon. The seventh hour already qualifies for the description בין הערבים, (Exodus 12,6)

חלב חגי, a reference to the Passover; just as you are not allowed to leave over part of the meat which is yours to eat until morning, the parts which are consumed on the altar must likewise have been burned up before then.