The time difference is computed on the client side. So either the server stored the wrong creation date with the post, or your computer has a wrong time setting.
Some ideas to identify the issue: does it happen on other devices ? Is the full date when clicking on the date above the post also wrong ? If you know how to use the developer tools, is the UTC date correct in the API payload in the network tab? If you access the database directly, is the datetime column correct ? Do your web server and database servers use UTC timezone ?
