the past 20 minutes looking at your watch 
(ROOT (NP (NP (DT the) (JJ past) (CD 20) (NNS minutes)) (S (VP (VBG looking) (PP (IN at) (NP (PRP$ your) (NN watch)))))))
(ROOT (NP (NP (DT ) (JJ ) (CD ) (NNS )) (S (VP (VBG ) (PP (IN ) (NP (PRP$ ) (NN )))))))