Good UX/UI for scheduled reports sliding time window

You know how in many analytical tools one can schedule a report of a certain kind to be delivered every X days (or similar)? What are good UIs for setting what's the date range that the report is generated with?

Here are some examples from Google Analytics, the most puzzling option there is - what happens if you select a set custom date range, like from Sep 2nd to Sep 23rd and then schedule a weekly delivery. What would you expect the Sep 2nd-23rd range to be - a sliding window or a set date range?

Screenshots:

Custom Range - https://www.dropbox.com/s/mo1zd9h5z81pod9/CustomRange.png

Email Report - https://www.dropbox.com/s/tsa3kljemz5bykt/EmailReport.png