only half-an-hour long or 
(ROOT (FRAG (ADJP (NP (RB only) (NN half) (HYPH -) (DT an) (HYPH -) (NN hour)) (JJ long)) (CC or)))
(ROOT (FRAG (ADJP (NP (RB ) (NN ) (HYPH ) (DT ) (HYPH ) (NN )) (JJ )) (CC )))