how long would it take from beijing friendship hotel to great wall?

we are staying at beijing friendship hotel, in zhongguancun south st. in Haidian District, we have from 5 am til 12 noon on friday to see the great wall. we couldnt find a bus tour who would take us. we will hire a cab for 700 rmb both ways . which portion of the great wall is closest to the hotel, how long would it take from hotel to great wall? do we have enough time to be back to hotel by 12 noon?

pls advise .. thank you so much.