#!/usr/bin/perl
use warnings;
use strict;

my $infile  = $ARGV[ 0 ];
my $outfile = "sliced_$infile";

open my $INFILE,  '<', $infile  or die "Cannot open '$infile' $!";
open my $OUTFILE, '>', $outfile or die "Cannot open '$outfile' $!";

my %flights;
while ( <$INFILE> ) {
    my ( $hour, $rest ) = /(\d+):\d+(.+)/;
    push @{ $flights{ $hour } }, $rest;
    }

for my $hour ( keys %flights ) {
    my $interval = 60 / @{ $flights{ $hour } };
    for my $i ( 0 .. $#{ $flights{ $hour } } ) {
        printf $OUTFILE "%02d:%02d%s\n", $hour, $i * $interval, $flights{ $hour }[ 0 ];
        }
    }

__END__