You want to use advanced reports with the "run report multiple times" checkbox enabled. Basically you use that feature anytime you want to iterate over a list of items. In your case, you are trying to iterate over a list of dates.
So you need to create a list of dates sorted the way you want. So when you create an advanced report, on the advanced tab, either use a static list of dates, or select the date column from an existing query. Then use the filters button to set the date range. You don't need any other filters, and any summary data query should work if it has the date column. That will return a list of dates.
Then you configure the query for the main report as you want (site and bytes).
Thanks sroering, I'll give this a shot and report back.
Thanks for your help sroering.
I have got what I was after by creating two queries, one for Bytes and Site Name (used for the main query) and one just with the Date field (used for the running the report multiple times).
It is pretty basic, but does what we need.