Client should give player option to change the timestamp to follow server time. This could actually be used as the default option then client could have option for "change offset". And to go even further, you could make it so that 24 hr format is optional, as well as am/pm standard. Or just put in 'advanced' for php format.
This would never be the default option, the only benefit is for auth (and active ones at that). But yea why not.
It uses Qt, C++, and JavaScript, but not PHP; so you can't use a PHP feature, if that's what you mean.
Generally formatting timestamps follow similar characteristics in different language/library implementations and we could include Qt's implementation: http://qt-project.org/doc/qt-5.0/qtcore/qdatetime.html#toString Just have a possibility to input custom format in settings dialog.