If you want to change the date format to display your own date/time of a post you will have to modify in _main.php the parameters of

$Item->issue_time();

In the [url=http://doc.b2evolution.net/HEAD/evocore/_blogs---inc---_misc---_misc.funcs.php.html]documentation[/url] you will find that the format to use is YYYY-MM-DD HH:MM:SS. It's not really true, in fact you should use: YYYY-MM-DD h:m:s
hours, minutes and seconds should be in lowercase.

So, I think we need to correct b2evolution/blogs/inc/_misc/_misc.funcs.php, line 433 and 450

 * @param string MYSQL date YYYY-MM-DD HH:MM:SS

should be

 * @param string MYSQL date YYYY-MM-DD h:m:s