Beijing Hikers was mentioned amongst the other Things to Do if you're in Beijing for just 72 hours, in an article on the CNN Travel website.
Why 72 hours? Some travelers are now eligible for a 72-hour transit visa, so you can stay for three days in Beijing without having to go through the sometimes lengthy application process for a tourist visa.
They scheduled us for 8:00am on the second day – perfect!
Here's the relevant section; read the full article for more good tips about what to see and do in the city.
“If you're only in China for a brief visit and a trip to the Great Wall is on your gotta-do list, the best way to get there is to hire a driver or join a group tour.
The trip should take two to three hours, depending on which section you visit. Sections in the “wilder” parts of the Wall, such as Jinshanling or Jiankou, are unrestored and have fewer crowds.
Athletic types may want to join expat hikers for the day; Beijing Hikers frequently offers all-inclusive trips to the Wall at competitive prices.
Read the full article here: Beijing travel: 72 hours in the Chinese capital (CNN Travel website link)