The Kunena team has announce the arrival of Kunena 6.3.0 [K 6.3.0] in stable which is now available for download as a native Joomla extension for J! 4.4.x/5.0.x/5.1.x. This version addresses most of the issues that were discovered in K 6.2 and issues discovered during the last development stages of K 6.3
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I believe that it's fairly easy to add your own timestamp format (if not through the configuration panel, then by modify the PHP code - located in your Kunena template - to use your own format). We've had these questions asked before on the forum - maybe not for a year or so - and searching the forum for information will get you the answers just as fast as me spending time figuring out which PHP file controls the function.
Actually, a useful tip might be to look in the language file? Try there, maybe that's the answer?