Gadget export
To export the relativetime gadget, click on "Download" button, save the downloaded file, go to Special:Import on the destination wiki and upload it. Then add the following to MediaWiki:Gadgets-definition page:
* relativetime[ResourceLoader|actions=edit,view|dependencies=mediawiki.util|type=general|default]|relativetime.js
You must have appropriate permissions on the destination wiki (including the right to edit system messages) and import from file uploads must be enabled.