When you generate time periods for a financial model, all periods share detail level, which you define in the Time Period Setup Wizard. You detail level for individual years using the Detail in Year option.
Under Level of Detail, select a period that determines aggregate periods. For example, you can select Months without selecting Quarters or Halves—resulting in 12 months and the annual period. You can add the aggregate periods later, which, except for annual periods, are not automatically created .