how and when to visit the Mutianyu Great Wall?

You are suggested to go for the visit on weekends when there are less people. Here is the direction from your hotel to that section for your reference:

walk from your hotel for 5-8min to Anzhenxili bus stop to take Special Bus line 2 to Dongzhimen North. Ask the locals about the directions to Dongzhimen Outer, where two buses leave for the section directly. They leave at 10:00 and 12:00. You should get off at Mutianyuhuandao. Then walk around 3 minutes to find the ticket office ahead. It costs no more than CNY20 pe person for the whole single trip.

I read than there is more than one bus for go there Tourism 867 bus and the 916 bus, Do you k ow the frequency of both?they go all the days?

Thnaks in advance

The former tourist bus 867 has been canceld. Now only two schedules of bus no. 867 are in service at 10:00 and 12:00. While bus no. 916 has many schedules. It leaves from Dongzhimen to Huairou Bus Station during 6:00-21:00.