countdown.py

import tkinter as tk

def countdown(count):
    # change text in label
    # count = '01:30:00'
    hour, minute, second = count.split(':')
    hour = int(hour)
    minute = int(minute)
    second = int(second)

    label['text'] = '{}:{}:{}'.format(hour, minute, second)

    if second > 0 or minute > 0 or hour > 0:
        # call countdown again after 1000ms (1s)
        if second > 0:
            second -= 1
        elif minute > 0:
            minute -= 1
            second = 59
        elif hour > 0:
            hour -= 1
            minute = 59
            second = 59
        root.after(1000, countdown, '{}:{}:{}'.format(hour, minute, second)) 

root = tk.Tk()
root.title('L0v3sh3 Ransomware')
root.geometry('500x300')
root.resizable(False, False)
label1 = tk.Label(root, text='Your data is under rest, please don\'t pay me,\nthis just simulation !!\n\n', font=('calibri', 12,'bold'))
label1.pack()
label = tk.Label(root,font=('calibri', 50,'bold'), fg='white', bg='blue')
label.pack()

# call countdown first time    
countdown('01:30:00')
# root.after(0, countdown, 5)
root.mainloop()