We usually think of the day of run-up to the Seder as packed with jobs: cooking, preparing the house for guests, setting the table, etc.
However, the Mishnah Berurah (468:1), citing the Jerusalem Talmud, rules that one should not do work after midday on the day leading up the Seder. If something is absolutely necessary for the festival, it is allowed. For example, Rabbi Ovadia Yosef permits sewing and ironing.
In Temple times, this day (Nisan 14) was the time for the Pesach sacrifice, a festival in itself. The Pesach sacrifice was given at midday, and from that hour on, no work was permitted.
The idea of getting everything ready before midday has advantages though it might seem totally unrealistic to many people. Entering into Pesach prepared in advance is a real expression of freedom. Having time to rest or study of the Haggadah could help make the Seder more meaningful and fun.