The hijacking began between 8:51 and 8:54.
( ( The hijacking ) ( ( began ( between ( ( 8:51 and ) 8:54 ) ) ) . ) )
(ROOT (S (NP (DT The) (NN hijacking)) (VP (VBD began) (PP (IN between) (NP (CD 8:51) (CC and) (CD 8:54)))) (. .)))
Sometime between 8:51 and 8:54 the hijacking started on September 11, 2001
( ( Sometime ( between ( ( 8:51 and ) 8:54 ) ) ) ( ( the hijacking ) ( started ( on ( ( ( September 11 ) , ) 2001 ) ) ) ) )
(ROOT (FRAG (ADVP (RB Sometime) (PP (IN between) (NP (CD 8:51) (CC and) (CD 8:54)))) (NP (NP (DT the) (NN hijacking)) (VP (VBN started) (PP (IN on) (NP (NNP September) (CD 11) (, ,) (CD 2001)))))))