If you want to schedule a Report Builder to run every Monday morning at 08:00 in order to collect information about the previous week from Monday (00:00) to Friday (23:59), you need to choose Last Working Week as the Report Period.
If it is the last day of the month and you want to run a Report Builder now to collect information for that month, you need to choose This Calendar Month.
If you want to run a Report Builder to cover the period from 08:30 on September 1st, 2003 to 17:00 on September 26th, 2003, you must select absolute Start and End Dates.
You want a Report Builder to run on the first day of each month from February 1st, 2004 to collect information about the previous month. You want each successive Report generated to build a cumulative record as the year progresses, for example, the first Report will cover January 2004, the second will cover both January and February and so on for the rest of the year. To achieve this, you must set the Start Date as absolute (1/1/2004 00:00). The End Date must be relative and set to be 1 day before the run time, it must end at the end of the day.