FCPX XML start and duration values ignore decimals e.g. duration='32.56s' would be interpreted as duration='32s', causing clip inaccuracies. This fix is to make these values fractions where the first number is the number of frames for the startTime/duration, the second number (2500) relates to the frame rate (25 frames per second). So dividing the total frames by the frame rate gets us the total seconds. You can read more about it here: https://www.fcp.co/final-cut-pro/tutorials/1912-demystifying-final-cut-pro-xmls-by-philip-hodgetts-and-gregory-clarke
note: if duration time is not divisible by 100, it seems to give a clip boundary warning in FCP, so have rounded this value