Classifieds Plugin :(Default custom field) Duration/Expiry FIELD TYPE

Classifieds Plugin : Duration/Expiry FIELD TYPE change not corresponding.

In the classifieds plugin, under custom fields, the default custom field is " Duration"

When I edit the Field type of this custom field to "Date picker ",
the information does not correspond.
( especially to the standard )

I have laid access to the site to review.

Your help will be immensely appreciated.