day 1   |    day 2
     ----  |
  -------- |
    -------|
       ----|--
      -----|--
       ----|---
         --|----
           |------
           | -------

##</code><code>##

my @now = localtime;
my $hour = $now[2];
$now[$_] = 0 for 0..2; # set hour, min, sec to 0;
$daychange = timelocal(@now);
# add one days seconds if running before midnight
$daychange += 86400 if $hour > 2;

##</code><code>##

    $sum{ $daystamp <= $stoptime ? 'first' : 'second' } += $linesum;