as a techie/programmer/databasey kinda guy, i only ever use
(& if needed hh:mi:ss
which is a close as i can get to ANSI standard whilst using punctuation to make it readable by a human bean.
using different formats is a right pain to code, especially when you're running it through a cobol program which is looking at trillions of iterations(passes thru the code).
once you've been through an exercise of making a 10k line program like this more efficient you tend to change your ways a little.
...and dont even get me started on people using 2 digit years instead of 4 GRRRRrrrrr
but it did keep me employed for a couple of years modifying programs to be Y2K compliant.
apologies to any non techies reading this.