Unpublished Enrollment Periods are not visible on the Enroll Form. By default, newly created or duplicated Enrollment Periods are unpublished.
When you are ready for them to be used, simply publish them. To do this, after creating a new Enrollment Period, click the cog and click the "eye" to publish an enrollment period.
To unpublish an Enrollment Period, click the cog and the "eye." When the eye is crossed out, that means the Enrollment Period is unpublished.