I did as a data source filter (not fully sure yet that this is optimal instead of doing it on the separat objects) with the following filter:
Månad is my date variable in my data, its character with the format YYYYMM. Månad_from is my from-parameter and Månad_tom is my to-parameter.
You add the drop-down to the report area, not the report or section prompt areas!
If you want to have the drop downs in the report/section area you need to have a separate dataset with the date values, otherwise both from and to will filter the data and you will just get the common date between them 🙂
//Fredrik