Date & Time in tkinter Window

import tkinter  as tk 
from tkinter import ttk
my_w = tk.Tk()
my_w.geometry("405x170")  
from time import strftime
def my_time():
    time_string = strftime('%H:%M:%S %p') # time format 
    l1.config(text=time_string)
    l1.after(1000,my_time) # time delay of 1000 milliseconds 
	
my_font=('times',52,'bold') # display size and style

l1=tk.Label(my_w,font=my_font,bg='yellow')
l1.grid(row=1,column=1,padx=5,pady=25)

my_time()
my_w.mainloop()

Managing Clock display format

time_string = strftime('%H:%M:%S %p \n %d %B')

time_string = strftime('%H:%M:%S %p \n %x')

time_string = strftime('%H:%M:%S %p \n %A \n %x')

Adding time to Entry box on Button click

import tkinter  as tk 
from tkinter import ttk
my_w = tk.Tk()
my_w.geometry("300x140")  
from time import strftime
def my_time(): # On button click 
    time_string = strftime('%H:%M:%S %p')
    e1_str.set(time_string)  # adding time to Entry

l1 = tk.Label(my_w,  text='Add Time', width=10 ) 
l1.grid(row=1,column=1,padx=10,pady=30) 
e1_str=tk.StringVar()
e1 = tk.Entry(my_w, textvariable=e1_str,width=15) #  Entry box
e1.grid(row=1,column=2) 

b1 = tk.Button(my_w, text='Update', width=8,bg='yellow',
     command=lambda: my_time())
b1.grid(row=1,column=3)

my_w.mainloop()

List of formats used for generating date and time