how long would it take from sheraton doncheng hotel to the summer palace in metro?

Hi, the closest metro station from your hotel is Anzhenmen, which is around 1.4km away. So you can take a taxi or walk there. Then use metro line 10 and transfer to line 4 at Haidianhuangzhuang and get off at Beigongmen. The metro duration is around half an hour.

As you know, both of them are worthwhile. If you prefer the natural scenery and wanna know more of the leisure life of the imperial family, go to the garden. If you wanna know more of Chinese imperial history and see the tombs of the emperors, the Ming Tombs are recommended.