Pardon my confusion, but did you expect the mtime to different or the same?

You seem to be reporting the results of several run. And the way the code is currently constituted you are only getting the mtime of the 'last' file in the directory; perhaps the stat and its friends belong a few line further up? Inside the while loop, perhaps?

If your question is why are several of the times the same, I should point out the mtime is the last -modified- time; not necessarily the creation time.