Hello,
I desperately try to find the way to make K2 display item and category (especially default and default_article.php of K2 component as far as i could understand) with the desired format, without comma neither hour/second, and i first set the the parameter in calling files at K2_DATE_FORMAT_LC2 (and not LC3 as it comes to happen), and in init files .ini of languages directory, I set the desired format in this variable ('l j F Y').
whatever i do, the date always displays on the following format "day, 0x month year hour secondd (idem regarding K2_content module). It's all the more frustrating that this setting of DATE_FORMAT_LC2 works well for Joomla items. Please note that i checked that the problem doesn't come from the template, that's K2 which is responsible for the date display.
I also find it astonishing that there are only a couple of remarks about that issue around the world (ad mostly with no proper answers).

I would be very grateful to the people who could help me and the whole community about hat issue.

Philippe

Did you try using Joomla!'s language overrides?
Also if the language overrides do not do the trick, this means that the template you are using, has the date format hardcoded.