For folders and video files, we choose the date the file was created. For movies we choose the earliest created date on any of the movie parts.
So, for example, if you have a movie which is composed of part1.avi and part2.avi, we will choose the earliest created date of those two files.
On windows machines, created date is not the same as modified date. This can be confusing when you expect a movie to show up in a certain order based on when you add it to your collection. The created date is exactly that, when the file was created…not when it was last modified or copied. In order to change this date (once the file has been created) you will need to use a third party tool. There is a freeware one called Attribute Changer that works well, but there are also many others available. Google can help you find them.
Keep in mind Linux file systems have no concept of “Date Created”, for these file systems “Date Created” is the same as “Date Modified”