FRC countdown - python countdown.py <unix timestamp>

countdown.py

import time
from Tkinter import *
import sys

END = int(sys.argv[1]) # epoch in seconds
RATE = 50
font1 = ("Helvetica", 30, 'bold')
font2 = ("Helvetica", 28)

root = Tk()

days = IntVar()
hrs = IntVar()
mins = IntVar()
secs = IntVar()
msecs = IntVar()

lbl_days = Label(root, textvariable=days, font=font1, width=3)
lbl_dayl = Label(root, text='days', font=font2)
lbl_hrs = Label(root, textvariable=hrs, font=font1, width=2)
lbl_hrl = Label(root, text='hrs', font=font2)
lbl_mins = Label(root, textvariable=mins, font=font1, width=2)
lbl_minl = Label(root, text='mins', font=font2)
lbl_secs = Label(root, textvariable=secs, font=font1, width=2)
lbl_secl = Label(root, text='secs', font=font2)
lbl_msecs = Label(root, textvariable=msecs, font=font1, width=4)
lbl_msecl = Label(root, text='ms', font=font2)

lbl_days.grid(row=0,column=0)
lbl_dayl.grid(row=0,column=1)
lbl_hrs.grid(row=0,column=2)
lbl_hrl.grid(row=0,column=3)
lbl_mins.grid(row=0,column=4)
lbl_minl.grid(row=0,column=5)
lbl_secs.grid(row=0,column=6)
lbl_secl.grid(row=0,column=7)
lbl_msecs.grid(row=0,column=8)
lbl_msecl.grid(row=0,column=9,sticky=E)

lbl2 = Label(root, text="countdown", font=font2)
lbl2.grid(row=1,column=0,columnspan=7,sticky=E)

#root.geometry('550x80')

def update():
	diff = END-time.time()
	stime = time.gmtime(diff)
	msec = int((diff%1)*1000)
	days.set(stime.tm_yday-1) # can only be less than a year
	hrs.set(stime.tm_hour)
	mins.set(stime.tm_min)
	secs.set(stime.tm_sec)
	msecs.set(msec)

	root.after(RATE,update)

root.after(RATE,update)

root.mainloop()

Hi,
I'm attempting to understand your code - but I'm getting an error when I attempt to run it:
File "/home/pi/Downloads/Countdown.py", line 5, in
END = int(sys.argv[1]) # epoch in seconds
IndexError: list index out of range

Any chance you could explain this as I'm struggling...

Py 2.7 or 3, Pi 3