I've done a little reading about time metadata in photos recently and learned that EXIF has a sub-seconds field (SubSecTime) that can store values which separately from where timestamps for year, month, day, hours, minutes, and seconds are stored. I've seen up to three digits stored here, looking around the web, which is thousandths of a second.
In cases where a good DSLR is being used with adequate lighting, shooting in burst mode it is entirely possible that multiple photos are being captured per second (which will all have the same value for DateTime / DateTimeDigitized / DateTimeOriginal).
Another case where this would be a factor would be when dealing with video frames which have been properly tagged. http://bit.ly/psfvftime
I ask because in an earlier discussion, Mike on the team was quoted as saying about a troubled synth, "...the time ordering was deemed unusable. There are multiple images with timestamp 1387624011 (i.e., 2013:12:21 11:06:51)...".