Did you make sure both your cameras are time synchronised? If not, you can do it after the shoot, just follow the advice above about shooting the clock with both. Find out how much they are off, and adjust the photos from one that is off in the matter described. If you followed my advice, your cameras would have different file base names already, if not, you can do Search by camera serial number or type or whatever that makes them different in PM, which will select only the files from the camera you searched for, and now you can use the Adjust capture time & date function inside PM to adjust their time by the exact offset you found out.