Keeping track of the difference and the closest time might be easier e.g

my $ctime = (stat($key))[10];
my($diff, $closest) = $ctime;
for(@returns) {
  $closest = $_ and $diff = abs($ctime - $_)
    if abs($ctime - $_) < $diff;
}
print "closest match is - $closest\n";
[download]

The code is untested, but it should give you something to work with, and saves having to keep a hash around of all the differences and times.
HTH

_________
broquaint