At 9:57, the passenger assault began.
( ( At 9:57 ) ( , ( ( the ( passenger assault ) ) ( began . ) ) ) )
(ROOT (S (PP (IN At) (NP (CD 9:57))) (, ,) (NP (DT the) (NN passenger) (NN assault)) (VP (VBD began)) (. .)))
The passengers started fighting back at 9.57.
( ( The passengers ) ( ( started ( ( fighting back ) ( at 9.57 ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS passengers)) (VP (VBD started) (S (VP (VBG fighting) (PRT (RP back)) (PP (IN at) (NP (CD 9.57)))))) (. .)))