They’re from the information the camera returns for the MTP object (file), which in turn typically come from the encoded timestamp for the file on the filesystem on the media card. Airnef doesn’t presently look at any EXIF data in files. I should mention Nikon presently has a bug on some cameras where the seconds portion of the MTP timestamp is always half what it actually is for the file – it’s a very odd bug. For example instead of reporting 16:34:36 for a file the camera reports 16:34:18 to an MTP client like Airnef. Or instead of 16:34:10 it reports 16:34:05. The camera reports the correct time when viewed in the playback menu and the actual filetime is correct – only the time returned to MTP clients has the issue.