Highlights of this feature:
You would manage this feature within any fee based price plan within the COST SPECIFICS admin tool page for that feature. Here is the full click path:
PRICING > PRICE PLANS HOME > [EDIT] (next to price plan to edit > COST SPECIFICS
You would look for the following section in the COST SPECIFICS admin tool page:
To select "charge by duration" for users attached to that price plan:
After clicking the edit listing duration choices link you would see a page like:
You would do these to insert a duration choice and delete one:
The above points you to the price plan wide settings. You can also set this feature up on a category by category basis within each fee based price plan as linked here:
PRICING > PRICE PLANS HOME > [EDIT] (next to price plan to edit > CATEGORY SPECIFIC COSTS > (SELECT CATEGORY) (see setting up category specific pricing to set)