Final answer:
Fixed-time period inventory models indeed allow for order quantities to vary with each time period based on changing usage rates, so the statement is true.
Step-by-step explanation:
The statement that fixed-time period inventory models generate order quantities that may vary from time period to time period, depending on the usage rate, is true. This type of inventory management system schedules orders at regular intervals (the fixed-time period), but the quantity ordered can fluctuate based on the consumption rate during each period. Unlike fixed-quantity systems where the same amount is ordered each time, a fixed-time system adjusts to changes in demand, hence the quantities ordered during each period may not be consistent.