This is more of a brainstorm rather than an answer, but how about a scrollable, horizontal timeline-like widget? The problem some people have with calendar displays is that it requires navigation in two dimensions, and/or they need to specify ranges that span months which can be very awkward with traditional month-at-a-time calendar widgets.
Present a horizontal row of boxes representing a typical period of time (two weeks?) plus a fudge factor. Let the control be scrollable, so there's a couple months worth of buffer on either side that can be scrolled to. for example:
(the , etc would be represented as a square or button -- don't use the square brackets, of course)
You can use color coding to represent weeks or weekends, or mondays, etc. It depends a bit on the actual application as to what makes the most sense to highlight.
If they are always selecting a continuous range, a single click sets the original beginning/ending of the range. Clicking to the right sets the end, clicking to the left resets the beginning. Two clicks and you're done.
You can also add controls to select common durations such as 1d, 1w, 2w, 4w, etc.
If they know the duration (eg: 2 weeks) but not the starting and ending dates, give them a way to select the duration and you can automatically select the end date based on what start date they pick.
Whether this is suitable for your app is hard to say, but it might be worth a paper prototype to show to stakeholders.