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

open FIN,  '<', 'something.csv'     or die "Cannot open 'something.csv' because: $!";
open FOUT, '>', 'something_new.csv' or die "Cannot open 'something_new.csv' because: $!";

my %data;
while ( <FIN> ) {
    next unless /^(\d+):(\d+):\d+\s+(\d+)$/;
    my $key = sprintf '%02d%02d', $1, int( $2 / 5 ) * 5;
    if ( exists $data{ $key } ) {
        $data{ $key } = [ $., $_, $3 ] if $data{ $key }[ 2 ] < $3;
        }
    else {
        $data{ $key } = [ $., $_, $3 ];
        }
    }

print FOUT map $_->[ 1 ], sort { $a->[ 0 ] <=> $b->[ 0 ] } values %data;