Quite a while ago I dug up the sources for mc-4.6.1 and started looking for a way to change the display format.
I came up with a patch (see attachments to this message) which successfully gave me the time format displayed the way I wanted in mc.
The other way is to edit the lines "timeformat..." to "..=%F %R" (man strftime) within '../.config/mc/ini' for the user knoppix and for root. Close the terminal and start again a terminal to have the changed datetime format.