Label.Place did not work?

[buran]

To expand on my previous answer, because there is same issue present here.
when you create infinite loop like the one on lines 15-16 you block the execution of the program further. i.e. you never reach/start tkinter mainloop on line 18

you need to define function and call it periodically using Tk..after() method

from tkinter import *
import time
 
win = Tk()
win.attributes('-fullscreen', True)
win.configure(bg='black')
 
T = StringVar()
T.set("88:88:88")
 
lab1=Label(win, textvariable=T, font=('DIGITAL DISMAY', 50), fg="blue", bg="black") # 
lab1.place(x=10,y=10)
lab1.pack()
 
def update_clock():
    T.set(time.strftime("%H:%M:%S"))
    win.after(1000, update_clock)
 
update_clock()
win.mainloop()

no need to say that it will be better if you use class

https://stackoverflow.com/a/459131/4046632