I guess they did it for clarity's sake - having several clocks showing at once may be confusing to some players (plus I think they're trying to cut down on the amount of clutter in the interface - I mean they've been consistently streamlining the menu buttons since launch). Unfortunately though, FFXI didn't have a dual clock display mode either so I doubt sadly SE will implement such a feature here.

If you have a mobile/cell phone you could always set the irl clock to display and just glance at it when you need to. Or else you could run the game in full screen bordered mode and have the taskbar visible, thus displaying the computer's clock, but I admit I'm just grabbing at bubbles here...