Editing custom fields in classifieds plugin

When I navigate to classifieds/content types/custom field I find 2 out-of-the-box custom fields
1) duration
2) cost

I have some questions around customer fields with the classifieds plugin

Humans tend to be myopic and my end users are service providers, so they may confuse the duration of the service they provide ( 1 hour massage or 6 month lease ) with the duration of the ad. I tried to edit the field description with help text, "How long would you like to run this ad?". Once I click on "Update Custom Field" the edits are not reflected.

On a related note, I would like users to be able to run ads for 6 months and a year. Through the front end classifieds/content types/custom field/duration, I tried "adding another option". Once I click on "update custom field" the added option was not reflected.

Will I need to make these changes from the backend?

Also for clarification, the "cost" custom field that comes out-of-the-box with the classifieds plug-in is the price the user lists with the ad and is not related to the cost of publishing the ad, correct?