Here's yet another WTDI:

This solution maintains a queue/array of size N (ie. store the names of the newest 5 files)

Linearly traverse the directory structure
  Compare timestamp of current file to timestamp of oldest/last item i
+n queue
  If file is newer
    Seek (the sorted) insertion point in the queue, and insert via spl
+ice
    If queue size > N
      pop off the oldest element from the queue
Repeat until finished...
[download]

When finished, you'll have a sorted array containing the newest 5 files

Update: BTW, you'll need to save the appropriate stat info for each queue element