[jepler]

I wonder whether you still have a bug. It depends how "scanning" is implemented.

    23:55 start scanning
    23:59:59 message added
    00:00:01 perform timestamp check

If there is the possibility of a message being added very late, and either being omitted from the scan that started earlier, or a delay from finishing the scan to performing the timestamp check, you might still miss a message.

You also mentioned a directory being created 5 minutes early: what if some system has a clock skewed the opposite way, and puts a message in a directory 5 minutes late instead?