We should have the option to

a) filter to view only actions that are "due" within the custom time frame OR

b) to view only actions that are "to be worked on" within the custom time frame, i.e. whose duration defined by start and due date includes the custom time frame OR

c) to view actions that are due or to be worked on in within the custom time frame.

At this time, the dates filter selects all actions according to c).