I was at the wall last week in the Badaling section. You can take the shuttle train from the beijing north train station at 930. although there is only one train in the morning and one in the afternoon, we were able to climb to the 12th tower (the highest point) and back and have lunch before returning to catch the train at 330pm. there are plenty of buses traveling back to beijing if you happen to miss the train. The weather was beautiful but super windy...