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