Hi Raju,
you can create a Restricted key figure / Selection to achieve the buckets (days)
Restricted key figure -- drag and drop key figure (ex: total) ->then document date, now restrict the document date with variable range using offset values . you can use the standard variable 0DAT (current date) when applying offsets.
ex: 0Dat-30 to 0dat . this give the the value of last 30 days. similarly you can apply it for other days.