use DateTimeX::Auto 0.003 qw/:auto/;

my $from = '2010-06-01';
my $to   = '2011-01-01';

my $diff  = $to->delta_days($from)->in_units('days');

my $mid_date_1 = $from->clone->add(days => $diff/3);
my $mid_date_2 = $to->clone->subtract(days => $diff/3);

print <<OUT;
from:   $from
mid 1:  $mid_date_1
mid 2:  $mid_date_2
to:     $to
OUT