Hi I have 12 hours transit in Beijing and I like to visit Summer Palace in 25 December Monday .

You are suggested to take Airport Express and transfer to metro line 10 at Sanyuanqiao; do another transfer to line 4 at Haidian Huangzhuang, get off at Beigongmen from Exit D. Walk west for about 5 minutes, you will get to the tickets window. It takes about 1h 20 minutes and CNY33.

As for great wall, I’ll take Badaling as an example. The time is a little rushing.
You can take metro line 4 and transfer to line 10 at Haidian Huangzhuang, do another transfer to line 13 at Zhichun Rd, and then get off at Huoying from Exit G4. Walk east for 5 minutes to Huangtudian Railway Station and take train S2 to Badaling. It takes about 2h 30 minutes and CNY12.

Thanks for your quick reply and good advice.