I suspect you'd have to wait a bit more than an hour. Given this:

#!/usr/bin/perl -w
use strict;
use Benchmark qw/:all/;
use Math::BigFloat;

cmpthese(
    1, {
        '2**10' =>  sub { my $x = Math::BigFloat->new(2**10); my $prod
+uct = $x->copy(); $product->bfac(); },
        '2**11' =>  sub { my $x = Math::BigFloat->new(2**11); my $prod
+uct = $x->copy(); $product->bfac(); },
        '2**12' =>  sub { my $x = Math::BigFloat->new(2**12); my $prod
+uct = $x->copy(); $product->bfac(); },
        '2**13' =>  sub { my $x = Math::BigFloat->new(2**13); my $prod
+uct = $x->copy(); $product->bfac(); },
        '2**14' =>  sub { my $x = Math::BigFloat->new(2**14); my $prod
+uct = $x->copy(); $product->bfac(); }

    });
[download]

I get run times like these:

      s/iter  2**14  2**13  2**12  2**11  2**10
2**14    139     --   -78%   -97%   -99%  -100%
2**13   31.3   345%     --   -88%   -97%   -99%
2**12   3.88  3488%   706%     --   -78%   -95%
2**11  0.870 15902%  3493%   346%     --   -76%
2**10  0.210 66195% 14786%  1748%   314%     --
[download]

With that kind of progression, 2**128 is, um, likely to take a while. :)