Determine quietest period for SQL server maintenance

I need a T-SQL statement written to determine when our database is at it's busiest and quietest times. We would like to schedule a maintenance window during the quiet time. The range of the data to analyse would span over the last 3 months. Many thanks in advance. It is a MSSQL database. The output of the report would be raw data that I can use to build an Excel spreadsheet.

The budget for this project is $50USD.