Assuming your data files hold the values in the more natural 'lines of pairs' arrangement, something like this might work for you:

#!/usr/bin/perl
use strict;
use GD::Graph::bars3d;
use Date::Calc qw(:all);
use GD::Graph::Data;

my ($d,$m,$y) = (localtime)[3,4,5];
my $mdy = sprintf '%02d-%02d-%02d', $d, $m+1, $y+1900;
my $title="IPTV - Video Server Bandwidth Report del "."$mdy";

my @data;
while( <DATA> ) {
    my @pair = split;
    push @{ $data[0] }, $pair[0];
    push @{ $data[1] }, $pair[1];
}

my $graph = new GD::Graph::bars3d( 1000, 500 );

$graph->set(
    x_label => 'Intervallo Orario',
    y_label => 'Traffico in Mbit/s',
    title => $title,
    x_labels_vertical => 1,
    x_label_position => 1/2,
    y_tick_number => 10,
    y_label_skip => 1,
    x_label_skip => 1,
    x_all_ticks => 1,
    x_labels_vertical => 1,
    box_axis => 0,
    y_long_ticks => 1,
    dclrs => [ qw(green) ],
    borderclrs => [ qw(black) ],
#white,lgray,gray,dgray,black,lblue,blue,dblue,gold,lyellow,yellow,dye
+llow,lgreen,green,dgreen,lred,red,dred,lpurple,purple,dpurple,lorange
+,orange,pink,dpink,marine,cyan,lbrown,dbrown
    show_values => 1,
    values_vertical => 1,
    values_space => 15,
    bar_spacing => 10,
    );
my $gd = $graph->set_values_font(GD::gdGiantFont);
my $gd = $graph->set_title_font(GD::gdGiantFont);
my $gd = $graph->set_x_label_font(GD::gdGiantFont);
my $gd = $graph->set_y_label_font(GD::gdGiantFont);
my $gd = $graph->set_x_axis_font(GD::gdGiantFont);
my $gd = $graph->set_y_axis_font(GD::gdGiantFont);

my $gd = $graph->plot( \@data );

open(IMG, '>file.jpeg') or die $!;
binmode IMG;
print IMG $gd->jpeg;
close IMG;

__DATA__
00:00    2585.54
01:00    Z095.44
02:00    1748.02
03:00    1454.55
04:00    1290.86
05:00    1235.33
06:00    1151.04
07:00    1160.86
08:00    1191.82
09:00    1343
10:00    1514.33
11:00    1693.67
12:00    1773.7
13:00    1897.82
14:00    2733.04
15:00    3257.12
16:00    3375.69
17:00    2949.53
18:00    2573.52
19:00    2139.65
20:00    1697.83
21:00    1989.94
22:00    2746.92
23:00    2998.7
[download]