I often find myself working with statistics that are time-indexed, and as such I put the data into a hash with the time as the key. I just stumbled over this tidbit to shorten the code it takes to increment a time key. The code to extend this to days, months, and years gets really hairy (I will post it too if desired).

$start = "23:58:45";
$end   = "00:01:15";
$key = $start;
while ($key ne $end) {
   print "$key\n"; # perform action on $hash{$key} here
   ($h, $m, $s) = split(":",$key);
   (($s +=1) %=60) || (($m +=1) %=60) || (($h +=1) %=24); 
   $key = join(":",map{sprintf("%02d",$_)}($h,$m,$s));
}
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