As soon as the clay has stiffened enough not to deform, the lid should be placed on the jar. Since the clay is still fairly damp, there is a possibility that the clay may stick the lid and jar together.
To avoid this, tear strips of paper towel and lay them across the rim and gallery on the jar. I prefer to cover about 75 to 80% of the gallery's area, if not more.
Set the lid and jar aside and allow to dry to leather-hard.