Custom week counts/buckets

We run our reporting weeks from Saturday to Friday. I need to create things like counts per week of items that occured in that week. For example:

15 tickets opened 5/26/18 - 6/1/18

5 tickets opened 6/2/18 - 6/8/18

12 tickets opened 6/9/18 - 6/15/18

but continually going back in time until the data allows or I restrict in some other way. I can't seem to find a clear example of how to achieve this and any help would be appreciated since I need to filter on that week format for ALL of our reports/dashboards.

Thank you