Among the listed date & time formats, double-click a format the current date and/or time in which you want to insert to the active document.
In this window you can change both the Default Date Format and Default Time Format.
The current date in the Default Date Format can be quickly inserted to a document by pressing the Shift+Alt+D keys.
To insert the current time in the Default Time Format, press the Shift+Alt+T keys.
To change the Default Date Format,
To change the Default Time Format,