Your code and explanation is a little confusing, but here goes.

If you go off into a while() like that you will slow down the main loop drastically. How often do you need to check the time? Look at Tk::after in the Tk docs which will tell you how to include a delay loop or a repetitive loop in the Tk mainloop function.

To update the GUI, just use $mw->update(); where $mw is the MainWindow and the GUI elements will update. Put the update in the loop.

jdtoronto