Create a vb-script which opens your Excel workbook (maybe without displaying it at all), refreshes the query, and then saves and closes the workbook. And then run this script by Windows scheduled task.

Btw. Why you need to automate this at all? When someone uses the workbook to see the data, then you can set the query to SQL Server to be refreshed on open. When you query the data in Excel workbook, then why not query the data from SQL Server directly?