How do we know that we are forbidden to eat hametz on the 14th of Nisan? TB Pesakhim 5

Yesterday's daf Pesakhim 4b quotes a Mishna from the upcoming daf Pesakhim 11b which details the debate between Rabbi Meir and Rabbi Yehuda when a person should stop eating hametz. The Gemara goes on to say that everybody agrees that one must not eat hametz by the beginning of the seventh hour. Remember these hours are what I call Jewish time or in Hebrew שעות זמניות. All the daylight hours are divided into 12 equal parts and all the nighttime hours are divided into 12 equal parts. That means that a summer daytime hour is longer than 60 minutes and a winter daytime hour is shorter then 60 minutes.

Because the Torah never explicitly prohibits the eating of hametz the day before Passover, the Gemara presents five attempts showing the Torah alludes to the cessation of eating hametz by the seventh hour on the 14th of Nisan. Starting on daf Pesakhim 4b and continuing on today's daf Pesakhim 5 provides the proof text from 4 amora'im and 3 tanna'im. There are only five different explanations why we are forbidden to eat hametz after the seventh hour because some of these proofs are duplicate. Although the amora'im disagree about some of the details, they all use the verse from Exodus 34:25. I shall cite only Rava's position found on today's daf.

“Rava said: The halakha that leaven is prohibited from midday on the fourteenth of Nisan is derived from here: “You shall not slaughter the blood of My offering over leavened bread; neither shall the offering of the feast of the Passover be left to the morning” (Exodus 34:25). This verse means that you shall not slaughter the Paschal lamb while your leavened bread is still intact. In other words, all leaven must be removed before the time the Paschal lamb may be slaughtered.” (Sefaria.org Translation) The first of three groups of pilgrims sacrifice their Paschal Lamb at the beginning of the seventh hour.

This year the 14th of Nisan falls on Saturday, March 27, 2021. According to the Vilna Gaon the daytime Jewish hour lasts for 62 minutes on erev Pesakh. Of course, there's a disagreement when the day actually begins which determines when you begin counting these hours. According to the Magan Avraham one must stop eating by 10:32 AM and according to the Vilna Gaon one must stop eating by 10:56 AM. Consult with your rabbi to find out which tradition your community is following.