my guess... don't bother with that option...the group name can be anything. Create a formula to evaluate the data (and as long as the data that is used in the formula is the datatable and available at the time the data is read...so no calling other formula/running totals/variables in memory) and group on that. Then you can display whatever verbiage you want...it can be from any formula.
Say your grouping formula is something like: (and say it has name of 'weekNo')
CINT((DAY({table.field})-1)/7 //this will give results0-4
CR can easily group on this value, for the display you would have a formula like:
else
"Week last days"
HTH
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