My reform family, in efforts to make sure that our 40 closest relatives can make it to our Passover seder, for the past few years has held the seder on the closest convenient date. This year, the "first night" seder at my house will be on Saturday following the Monday that is everyone else's first night. Is there anything in Jewish law that says this is a wrong/bad practice?

It is stated explicitly in Pesahim in the Talmud that the Seder is to take pace on the first night. Thus, any response based on Halachah (rabbinic law) will state that position.

 

Nevertheless, since the essence of Reform Judaism is the ultimate freedom of the individual to make his or her own decisions with regard to the issues of religion, the only limitation being that you cannot limit the freedom of another person, the decision remains yours.

 

You might be interested in knowing that this has been debated on our closed rabbinic listserve, with the majority of reform opinion being that the Seder should take place in the first night.

 

My personal opinion is that it is better for the Seder to take place on a different night than not at all.     

From an Orthodox/traditional perspective what you suggest is problematic. The celebration is done not to accomodate family, but, instead to bring one's family into the community of Israel by celebrating Judaism's founding event on the same day that Jews everywhere celebrate it. Having a Pesah experience when convenient does not create that sense of national solidarity that comes from sharing the same moment together with the entire community.

 

In addition, when convenience becomes the critical factor many important traditions and practices may be discarded or modified beyond recognition, and their impact may consequently be seriously attenuated. One of the tests as to whether something is truly valuable to us is our willingness to go to great lengths to make it happen.

 

Finally, Judaism has a concept of sacred time that suggests that there is a spifritual reality to the universe that is different on holy days. That sanctity requires that the celebration occur on the day except in some very rare and exceptional cases. That picture of time and its sacred seasons would not sustain approaching the question as you have

To answer your immediate question: “Is there anything wrong with this practice?,” the Torah addresses this very question in Numbers 9:6 ff., and establishes a holiday, Pesach Sheni, “Second Pesach” for those who could not celebrate at the appointed time. The Torah is explicit: Pesach Sheni was for those who were impure, and therefore could not offer the Pesach sacrifice, or for those who were travelling.