Is it possible to create a report that shows the number of worked days filtering by Month ?

Is it possible to create a report that shows the number of worked days filtering by Month ?

Good Morning just upgraded to Professional edition, we made  a lot of customizations to the potentials form, we are an aerospace consulting firm and we need to keep track of also the worked days of our consultants, so we added some custom fields to the Potentials (Project Start Date, project end date and duration (Formula) that obtains the difference from the first two entries. 

Is there a way when to generate a report to show the duration or worked days for a specific moth (e.g I have a potential work Won,  (DD/MM/YYYY) Start date 1/1/12 and End date 15/2/12 the formula field duration is equal 45 days. If I filter by Month say January I would like to see in duration 31 days is this possible ? all I get is the total duration no matter the filter in the report. Is there a way to accomplish this ? any tips would be appreciate it. If it can be done but is not easy and requires extra work we are willing to pay.

Regards, 

Nico