Hi Chris,
My timeline is based on the information given in the report for 12:45:34 and 12:45:39. That would put frame no. 296 at 12:45:01.
While I agree that one would expect the first 1245 frame at 12:45:00, that doesn't fit with the two points mentioned in the report. Maybe BEA's GMT's are one second off, but who cares? What matters are the seconds to some reference time in the recording. The report on page 10 also puts the impact with the trees between 12:45:39 and 12:45:40. The data clearly show a discontinuity between frames 334 and 335, so that fits also. Another fit is 114 kIAS at 'ts'.