I don't know about being *prettier*, but instead of join(), you could just concatenate them using the dot operator.

my $prettyFileTime = localtime((stat($dir.'/'.$file)))[9]);
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Which is how I'd write it. That only eliminates one function, which doesn't necessarily make it clearer, but a little more concise, none the less. You also might want to try breaking it up and calling stat() only if $dir.'/'.$file exists, else do something different.