Group by day - evaluation date formula question

Hello,

I am currently working on a report for on-call coverage. I am having difficulty grouping by date and I'm hoping someone can help me. Here is my situation.

The on-call database has a coverage start date and coverage end date.

Person A has a coverage start date of 9/1/2009 and a coverage end date of 10/5/2009.

Person B has a coverage start date of 9/15/2009 and a coverage end date of 10/10/2009.

The report I am trying to create needs to be grouped by the calendar day of coverage. What I mean is, I need to be able to evaluate the coverage for a particular day.

If I run the report for the evaluation date of 9/10/2009, it would show Person A, their coverage start date and coverage end date.

If I run the report for the evaluation date of 9/20/2009, it would show Person A and Person B, with their respective coverage start and end dates.

My question is, how do I create this evaluation date?

Since this is a report for on-call coverage, I will also need to run this evaluation date into the future to confirm that there aren't any gaps in coverage.

What I need to do is run this report for so the evaluation date would be for the next month. So if I ran the report today, it would show me the on call coverage for November 2009, grouped by day.

Any help you can provide would be greatly appreciated.