Creating time lapse images in python

The following code capture an image from webcam, and saves into the disk. I want to write a program which can automate capturing of an image at every 30 seconds until 12 hours. What is the best way to do that?

import cv2     
cap = cv2.VideoCapture(0)
image0 = cap.read()[1]
cv2.imwrite('image0.png', image0)

Following is the modification based on the answer from @John Zwinck, since I need also to write the image captured every 30 seconds into the disk naming with the time captured:

import time, cv2
current_time = time.time()
endtime = current_time + 12*60*60
cap = cv2.VideoCapture(0)
while current_time < endtime:    
    img = cap.read()[1]
    cv2.imwrite('img_{}.png'.format(current_time), img)
    time.sleep(30)

However, above code could write only the last file over the previous one for each time. Looking for its improvement.

Solution

import time
endTime = time.time() + 12*60*60 # 12 hours from now
while time.time() < endTime:
    captureImage()
    time.sleep(30)