Code:
# str8.py
#   Program to count time from a certain event

from tkinter import *
from datetime import *
from threading import *

root = Tk()
root.title("STR8")
root.resizable(width=False, height=False)


def main():
    print_it()


def stop():
    root.destroy()


def display():
    event, today, str8, seconds, minutes, hours, days, weeks, years = calc()
    Label(root,
          text="You have been STR8 for:\n",
          font="Verdana 8 bold").grid(row=0, sticky=W)
    Label(root,
          text="Years: "
               + str(round(years, 2)),
          font="Verdana 8").grid(row=1, sticky=W)
    Label(root,
          text="Weeks: "
               + str(round(weeks, 2)),
          font="Verdana 8").grid(row=2, sticky=W)
    Label(root,
          text="Days: "
               + str(round(days, 2)),
          font="Verdana 8").grid(row=3, sticky=W)
    Label(root,
          text="Hours: "
               + str(round(hours, 2)),
          font="Verdana 8").grid(row=4, sticky=W)
    Label(root,
          text="Minutes: "
               + str(round(minutes, 2)),
          font="Verdana 8").grid(row=5, sticky=W)
    Label(root,
          text="Seconds: "
               + str(round(str8.total_seconds())),
          font="Verdana 8").grid(row=6, sticky=W)
    Button(root,
           text="EXIT",
           font="Verdana 8",
           height=1,
           width=19,
           command=stop).grid(row=7)


def calc():
    event = datetime(2017, 3, 29, 13, 45, 0)
    today = datetime.now()

    str8 = today - event

    seconds = str8.total_seconds()
    minutes = str8.total_seconds() / 60
    hours = minutes / 60
    days = hours / 24
    weeks = days / 7
    years = weeks / 52

    return event, today, str8, seconds, minutes, hours, days, weeks, years


def print_it():
    t = Timer(1.0, print_it)
    calc()
    try:
        display()
    except RuntimeError:
        pass
    else:
        t.start()


main()
root.mainloop()