How it works
When DST is active or DST ends, Windows will report file's time with exactly one hour difference. If you perform a comparison with different file systems, you may notice files become newer suddenly (if you disable Automatically ignore DST difference).
When enabled, Comparator Fast will check if both files have the same size, and if the timestamp (date/time) is exactly one hour, it process the file as the same. If you modified a file, is almost impossible it may have exactly one hour difference (including milliseconds), so this method is secure and accepted.