Before b1708, the effective date for publishing to EC could only be updated in the xml.
Or via the use of custom fields and mapping (see the "see also" section below)
Since b1708 however, in the section "Employee Central Settings" under the template setting section now allows for this date to be updated in the UI
To update the publishing date, go to "Employee Central Settings" under the template setting section.
And you will see the following screen
You can update the Effective date for Publishing here, and this will update the xml section "comp-ect-output-component"
comp-ect-output-component effectivedate , KBA , LOD-SF-CMP-ADM , Admin Tools, Settings, Permissions , LOD-SF-CMP-EC , EC data, config & settings within Compensation , How To