People still competing in the London Marathon days/weeks after the official race day was held?

Adam is absolutely right. The London marathon course is only open for 7 hours. After that the race is over and they advise runners to move to the sidewalk as the streets will re-open to traffic. But the timing devices and everything else would be taken down so there would be no official finishing. Marathons rent or lease the course from the local municipality for a specified period of time.