Hello,
When I set a release date for a version in the Manage Versions screen:
/plugins/servlet/project-config/{MY_PROJECT}/versions
Release Date = December 20
It shows one less day in the Releases screen that you can access from the sidebar:
/projects/{MY_PROJECT}?selectedItem=com.atlassian.jira.jira-projects-plugin:release-page
Release Date = December 19
Probably some timezone conversion bug?