How long does it take to get to Mutianyu from the Beijing Airport all together?

You mean Capital Airport, right? You may take Airport Express to Dongzhimen Station, Exit E. The fare is CNY 25, and the trip takes about 25 minutes. Then, take bus line 916 Express to Huairou Beidajie (about 1 hour). Upon arrival, take bus line h23 or h35 to Mutianyu Roundabout (about 50 minutes). Walk north, and you can see the ticket office. The whole trip takes about 2.5 hours.

Or, you can charter a car to the Wall from the airport. The fare may be around CNY 500 to 600 for a round trip. The trip takes about 1 to 1.5 hours. :)