It strikes me as remarkable that you say, right in your post, that you need them sorted by the timestamp in the filename, and then you say you tried stat(), which did exactly what the documentation says it does (which isn't parsing the filename). When you go so far as to specify the behavior, you should strive to write code that matches the specification. If you don't, you will continue to struggle at relatively simple programming tasks.

"I'm trying to parse this filename string. I tried stat()" is a little like saying "I just can't seem to drive this screw. I tried a hammer, but it didn't work."