sub hours_in_day {
    my $now = 60*60*int( shift()/60/60 );   # Start of this hour
    my $hour = ( localtime($now) )[2];
    $now -= $hour*60*60;                   # Start of this day
    $hour = ( localtime($now+24*60*60) )[2];
    $hour -= 24 if int($hour/12);
    return 24-$hour;
}