At any moment, you can retrieve the report for the previous eight whole weeks. This means that you can view data from Monday in the first week until the end of Sunday in the eighth week. If you're currently on Tuesday in the eighth week, you can view data from the previous seven weeks and two days.
Furthermore, we report the last 100.000 separate search terms, regardless of the period of the data. That means that the numbers for Times searched will keep counting, but no new search terms will be added.