Answer:
At the end of the period when determining inventory value and profit from sale.
Step-by-step explanation:
The Periodic inventory system keep track of value of inventory at the end of the period.
A credit on Inventory Account shows a decrease. Such decrease arise when inventory has been issued to customers.
Thus when it comes to periodic inventory system this entry is only done at the end of the period when adjusting inventory at the end of a period and recording cost of sales.