Tutorial:Change or customize date and time formats

Tutorial
They are saved in a plist file in /private/var/mobile/Library/Caches/DateFormats.plist

Copy this file to your PC or MAC, edit the formats in the file and copy back :-)

Unfortunately the file is in the binary plist format, so you may need to use a utility such as plutil to convert it to text, edit and then convert back to binary.

You can also change the way the calendar is displayed by changing the locale property in the same file.

PList Tools

 * A perl based version of plutil. This is a dos file so for use on Linux you have to first convert it to *nix format.
 * Notepad++ is a good tool for Windows