First, one had to designate the sheep to be eaten at the Seder early, three days in advance. There was a special procedure of sprinkling its blood on the lintel and the two doorposts using a hyssop bundle. In Egypt, this was to distinguish between the Jewish homes and the Egyptian homes, which would not apply to subsequent years.
The first Seder was conducted in haste, dressed and ready to go. Anybody who has been at the Seder nowadays knows that "whoever prolongs it is praiseworthy."
Art: Sheep and chickens in a barn Eugene Verboeckhoven