If you have custom K2 template overrides (perhaps done by someone else), these content elements may have been entirely stripped.

In any case, a URL to your site would help.

As you can see here www.drustvo-para-lj.si/bloggg?template=protostar the date/time displays just fine. Which means that whoever built your K2 template overrides just stripped off content they weren't using, even though it could have easily been disabled in K2's settings.

So compare your overrides with K2's default template overrides from /components/com_k2/templates/ and copy any missing parts. Shouldn't be hard to spot them.