I find the term "bucket" interesting....

I'm pretty sure that what you want is to simply group the report on the date.  When you do a group by date, Crystal allows you to group by common "buckets," such as week, month, or quarter.  Open Group Expert.  Add a group based on a date.  Click on the Options button.  At the bottom of the dialog box, you will see the option to group by one of a variety of date ranges.

If you need to group by a slightly more unconventional range, such as every 30 days before and/or after today's date, look at the date range constants in the help file (or, better yet, in Brian's book).  A lot of these are predefined in Crystal, so that you can write the formulas using them very easily.