#!/usr/bin/python

import time
import datetime

from Adafruit_LED_Backpack import SevenSegment

# ===========================================================================
# Clock Example
# ===========================================================================
segment = SevenSegment.SevenSegment(address=0x70)

# Initialize the display. Must be called once before using the display.
segment.begin()

print "Press CTRL+Z to exit"

# Continually update the time on a 4 char, 7-segment display
while(True):
  now = datetime.datetime.now()
  hour = now.hour 
  minute = now.minute
  second = now.second

  if hour >= 21 or hour < 7:
    segment.set_brightness(0)
  else:
    segment.set_brightness(4)
  
  if hour == 24:
    hour = 12 
  else:
    hour = hour % 12

  A = int(hour / 10)
  
  if A == 0:
    A = ' '

  segment.clear()
  # Set hours
  segment.set_digit(0, A)     # Tens
  segment.set_digit(1, hour % 10)          # Ones
  # Set minutes
  segment.set_digit(2, int(minute / 10))   # Tens
  segment.set_digit(3, minute % 10)        # Ones
  # Toggle colon
  segment.set_colon(second % 2)              # Toggle colon at 1Hz

  # Write the display buffer to the hardware.  This must be called to
  # update the actual display LEDs.
  segment.write_display()

  # Wait a quarter second (less than 1 second to prevent colon blinking getting$
  time.sleep(0.25)

@@ -718,10 +718,23 @@
  == 
-24
+12 or hour == 0
 :%0A  

Update clock.py