Can I use group filter in the RTC dashboard to group results by specific timeframes ?

Can I use the group filter option in the RTC dashboard WorkItem Statistic widget for grouping the result workitems to specific timeframes ?
e.g.
timeframe1: 16th jan to 15 feb
timeframe2: 16the feb to 15 march
...
depending on a datefield the WorkItem should be reported as be part of timeframe 1 or timeframe 2 in the summed result of the WorkItem Statistic widget result.

If this is not possible any other thought how to group this in one viewlet ?

Thanks in advance.
Siegfried.