Correction: An earlier version of this story misidentified Rabbi Daniel Freelander. The story has been corrected.

Sundown Monday signals the start of Passover, the most observed of Jewish holidays, a night when Jews follow the biblical mandate to gather, eat and retell their story of liberation. Unless, that is, they already did it over the weekend or plan to some other night this week.

Mostly to accommodate busy work and travel schedules, more American Jews are holding their Seders — the elaborate ritual meal at the heart of the eight-day holiday — on different nights, not only on the traditional first two nights.

Until now, the idea of bringing a do-it-yourself attitude to such a major and weighty holiday has carried too much stigma because of a perception that it is too unconventional or not legitimately Jewish, said rabbis, community leaders and Seder-holders. But that perspective is fading somewhat, and such Seders are frequently large, traditional and carefully crafted, even if they are far from the norm.

“When we first started [holding Seders on other nights], I argued with my sister. She said, ‘You’re not supposed to do this or that; you’re not Jewish,’ ” said Sharron Cristofar, 71, who will have 30 people at her Reston home on Saturday night. “But the thing is, what I most want to leave my kids and grandchildren is my legacy. What’s most important is to have that sense and memory of Passover.’’

Given the challenges of bringing people together from around the country, “the [correct] day is important if we can do it, but what’s more important is that we are together,” Cristofar said.

For Jews, tinkering with Passover is akin to changing when Christians celebrate Christmas, which — and this isn’t a coincidence — actually has been happening more as well, for similar reasons. Along with more Christians making Saturday night or some other non-Sunday slot their weekly church time, or Jews setting aside Sunday morning as their weekly time to go to synagogue, even if what they do is just take a class, because that’s when their children are in religious school. The Jewish Sabbath is Friday sundown to Saturday sundown.

And when it comes to Passover, it’s not only the convenience of gathering on the weekend that’s behind the loosening of the calendar. There is also the mushrooming of “theme Seders” held on nontraditional nights. Such Seders, which became well known in the 1960s and 1970s to promote social causes, weren’t meant to replace the traditional meal. But these days, some Jews use these Seders, which have expanded to focus on everything from gay rights to human trafficking, as their sole Passover observance.

Jews, including rabbis, are of varying minds on this rejiggering of an event that is one of the few rituals American Jews still overwhelmingly embrace.

On one hand, the Torah tells Jews to gather with family “on the eve of the holiday” and to tell their children the story of how God liberated them from slavery in Egypt. The Exodus story was so central to the story of Jews that in biblical times, the month of the Passover festival was the first month of the Jewish calendar. Later, the fall holiday of Rosh Hashanah became seen as the “new year.”

As far as the timing, there is both scriptural and communal power in knowing that Jews around the world are telling this story together on the same days and trying to hew closely to the words of the Torah.

On the other hand, most of how Seders are conducted was added later in history, and the larger point is to experience a rich revival of the values of Passover. Gathering at a time when more people can come and be less rushed may create a more meaningful experience that brings people closer to their Judaism, said rabbis and holders of alternative Seders.

“The first day is of special religious significance. But that doesn’t mean it’s the only time,” said Rabbi Daniel Freelander, a leader of the Reform Jewish movement, the largest part of U.S. Judaism. “If Passover takes on great meaning, it’s because it’s the one time you do a Jewish event in your home. It’s a new cycle of that religion.”

Shelley Schweitzer was fine with celebrating Hanukkah on nontraditional nights and changing around the traditional Passover recipes to accommodate the growing number of food allergies, vegans and vegetarians. (She includes a detailed ingredient list inside the Haggada, Passover’s ritual storytelling guide). But when Schweitzer’s longtime family Seder switched for the first time last year to the weekend to accommodate more far-flung millennials, she was so bothered that she went to her rabbi’s wife for counsel. Passover felt different, perhaps more serious.

Yet moving the Seder to this past Saturday night brought more people who had been away for years. For many of the 31 people in attendance, she said, this was their only Seder.

“The shift toward being together overrides the calendar,” said Schweitzer, 58, who works as a congregational organizer in Canton, Ohio.

She isn’t yet sure that she sees her Saturday Seder — which her son dubbed “Fassover,” or Fake Passover — as equal to the traditional nights. She will host a much smaller Seder on Monday with friends.

Rabbi Marc Katz of Brooklyn was invited to multiple Seders this year, including on the two traditional nights, which he will attend with his parents in Rhode Island. He says social-justice Seders have proliferated on nontraditional nights because Passover is the holiday most linked to the narrative of freedom. “There is this incredible empathy, this sense of putting yourself in the shoes of the stranger,” he said.

Katz says that having your only Seder on a nontraditional night is better than not having one at all, but he emphasizes the power of observing together and of guarding the Jewish calendar.

“There will always be a minority doing things for different reasons, but moving Jewish holidays will never be a movement,” Katz said of the shifted Seder dates.

Freelander noted that it initially was controversial for synagogues to make Friday night their worship night instead of Saturday morning. Friday night was supposed to be in the home. But now Friday night is mainstream as the sole worship time for millions of U.S. Jews.

The question arises across religions as to whether the loss of tradition can be offset by an infusion of new ideas and practices.

Katie Ashmore didn’t even know until recently that there were traditional Seder nights.

When she was growing up in New Jersey, her family’s tradition was to gather with her grandparents on a weekend during Passover. They used a Seder plate, a ritual item holding symbolic foods from the Passover story, and ate gefilte fish. Her grandfather would craft stories about Moses, but with people at the table playing his role as liberator through their jobs as labor lawyer, carpenter and human rights activist.

After her grandfather died, the Seder became more traditional in that they now have a Haggada, which is written by Ashmore’s mother, but it is still on the weekend. When she took a job at Jews United for Justice, where she is a community organizer in Montgomery County, Ashmore learned that most Jews hold their Seders on the first two nights.

“I’ve learned so much and appreciate the chag [holiday in Hebrew] days now. But Passover in particular is so communal, so I’m relying on friends and family to be there,” she said. On Monday night, she expects to be camping in Northern California.

Cristofar intends to be home cooking in Reston and doing last-minute preparations. A lay leader in her synagogue, she makes her own Haggadas and was playing with a vegan soup. But some things are not to be tinkered with.

“You don’t mess with my mother’s salad [recipe]. It’s very simple, like nothing — but it’s very important.”

Passover recipes: Brisket, matzoh and more