9
Just to keep this up-to-date, the first suggestion (main.php) works on xbb 3.05 without needing the second (user.php).
The original appears commented out & an alternative is below it.
//define("_MD_TODAY", "Today G:i:s");
//define("_MD_YESTERDAY", "Yes\te\rday G:i:s");
//define("_MD_MONTHDAY", "n/j G:i:s");
//define("_MD_YEARMONTHDAY", "Y/n/j G:i");
define("_MD_TODAY", "Today G:i");
define("_MD_YESTERDAY", "Yes\te\rday G:i");
define("_MD_MONTHDAY", "j/n/y G:i");
define("_MD_YEARMONTHDAY", "j/n/y G:i");