You should set up all the time periods that you require in advance including time periods well into the future.
To import time periods:
In this example several time periods of the type Week will be created:
Click the image to expand it.
For more information about importing data using the Salesforce Data Loader Tool, see the Salesforce documentation.
To create a single time period:
Concept Information
About Time Periods, Work Calendars and Holidays
Related Tasks
Reference Materials