When you're in the game menu, hold down both shoulder buttons while pressing start.
The year at the bottom will turn red.
Dpad L/R move between Y/M/D & Clock
Dpad U/D changes setting
Start again to get out.
There ya go!
Bob's yer uncle!
(always liked saying that)
Dag! Psyfira beat me to it, and I had to sit there and figure it out.... hmph!