Is it possible to build a line chart where the Graph by value is interval for 30 days
the current date is 15th jan
So the values are displayed by
create a Beast Mode ... this is pseudo code.
when Date >= today - 30 then 'Group 1'
when date >= 60 then 'Group 2'
Alternatively if you're using this logic a lot, build a date dimension ( a table with one row per day) in Magic or SQL and then add the '30 day trailing' column with similar logic from your beast mode.