Here's an example program in Python that uses the tkinter library to create a GUI window and display the current time:

```
import tkinter as tk
import time

def update_time():
    curr_time = time.strftime('%H:%M:%S')
    time_label.config(text=curr_time)
    time_label.after(1000, update_time)  # update every second

root = tk.Tk()
root.title("Current Time")

time_label = tk.Label(root, font=("Arial", 50))
time_label.pack(padx=20, pady=20)

update_time()  # start updating the time label

root.mainloop()
```

This program creates a window with a label that displays the current time in a large font. The `update_time` function gets the current time using Python's `time` module, updates the label's text, and schedules itself to run again in one second using the `after` method. Finally, the `mainloop` method starts the GUI event loop to handle user input and refresh the display.
Scrivere un programma per visualizzare l'ora in una finestra GUI.