Tkinter messagebox and using datetime/timedelta

[Kaltex]

Hi all

I made this really simple program for myself to remind me to take some breaks.


It works great and all, although there is one behavior that I did not expect and although I don't mind it so much, i'd like to understand why it happens.

When the while loop is going and an interval variable is passed, the messagebox will come up. However, until I close the messagebox, it won't repeatedly come up multiple times. In fact I believe even the 'if' statement does not come into play again until I close that message box. My questions are:

• Shouldn't multiple messageboxes be coming up based on the if statement? Wouldn't the loop constantly be going, meaning multiple boxes come up?
  
• Does everything stop (including the loop) when the messagebox comes up?
  

import datetime as dt
from tkinter import *

def setInterval():
    interval = dt.timedelta(minutes = int(entry_1.get()))
    StartTime = dt.datetime.now()
    while True:
        if dt.datetime.now() == StartTime + interval:
            messagebox.showinfo('STRETCH TIME',message = "Please take a stretch break!") 
            StartTime = dt.datetime.now()
    
        
    

if  __name__ == "__main__":
    root = Tk()
    intervariable = IntVar()
    theLabel = Label(root,text="Enter time below in minutes (e.g 30)")
    theLabel.pack()
    entry_1 = Entry(root)
    entry_1.pack()  
    button_1 = Button(root,text="Set interval",command=setInterval)
    button_1.pack()
    root.mainloop()

Appreciate any assistance :)