Probably nothing. I have received a few reports of time zone issues – cameras often do not put time zones into the file, so setting the time is not straightforward. Photos also has its own notion of time, which can conflict with the time in the file. Please email support@gentlemencoders.com and I can help you directly. I will need a sample file or two, but we need to do that over email not here (and I will send instructions over email as well for what I need).