What are the default dates set in the Unifyr Looker-generated Reports?

This is very dependant on the report. Some of the available dashboards have multiple date ranges (e.g last month and statistics from the last 12 months).

All reports display their relevant filters at the top of the report and can be selected to create a different view.

In the image below you can see the header of the Monthly Highlights dashboard. You can click Filters on the left to expand all of the filter values and change accordingly to customize the data being reported on.