Went this Monday. Got the S2 06.12 from Beijing North and back on the 11.50 which is plenty of time- the 10.50 was missing with the usual lack of explanation! . The 06.12 is almost completely empty on a Mon and the front 2 (Badaling end) coaches are declassified ex 1st class with 2 x 2 seats but with seat back tables removed. If you sit right up the front the diesel loco gives some amazing thrash through the tunnels on the very steep mountain passes. Don't forget it has a reverse zig zag just before Badaling which must be unique on a suburban service. The whole line is v.slow but has great views of other wall sections from the left side on the way up to Badaling.
Do not bother with the free bus from Badaling station they wait until completely rammed and drop you off at completely the wrong place where the rip off cable car is. Just walk the 10-15 mins up to the main ticket office located through the gatehouse walking past all the tourist shops, subway KFC etc. Once you get your ticket go through, turn left and go up the South wall. I had the place almost to myself and keep going as far as you can. I completely ignored the North Wall it is so crowded with tour groups and the 'money shot' is taken from tower 3 on the South side anyway.
You can use your Beijing transportation "oyster type" card so no aggro queuing buying a ticket. Don't also forget it will be much colder at Badaling than in Beijing especially if arriving early. The 6.12 is essential to avoid the worst of the tour groups and if you don't want to wait until the 11.50 you could catch the first 11.00 bus back.
If you have any sort of mobility issues do not begin to underestimate how steep and slippery most of the wall is- particularly if there is morning dew or if there has been rain. If you do the south side there is a poorly signposted exit route near the toilets by tower 3 which avoids the steepest parts coming back but brings you out past the ticketed area if you were intent on the North side. The South side cable car hasn't worked in years despite what you read on the internet.
You will find yourself being asked for photos all the time by folk from some remote parts of China who have never seen a non Asian person before its all part of the experience! The forecast was looking great for Beijing when I left for Shanghai this morning so you should be in for a good weekend.
Don't miss the old Ming era walls near Beijing station- they hardly get any visitors and has to be one of the greatest train viewing places on earth with endless movements out of high speed, shunting locos, sleepers ECS etc. There will invariably be a few Chinese gricers with their cameras up there too.