use warnings;
use strict;
use Data::Dumper;

my %Months = ( 'Jan' => '01',  'Feb' => '02',  'Mar' => '03', 'Apr' => '04', 
	'May' => '05',  'Jun' => '06',  'Jul' => '07', 'Aug' => '08',
	'Sep' => '09',  'Oct' => '10',  'Nov' => '11', 'Dec' => '12'  );

my ($Date1,$Date2) = ('Jul  3 2016 10:45 UTC','Aug 12 2017 11:56 EST');

my @Variables = ($Date1,$Date2);
for my $Date_Ref (@Variables) {
	my ($Month,$Day,$Year,$Time) = split ' ', $Date_Ref, 4;
	$Day = "0$Day" if length($Day) == 1;
	$Date_Ref = $Year."-".$Months{$Month}."-".$Day;
}

print Dumper \@Variables;

__END__

$VAR1 = [
          '2016-07-03',
          '2017-08-12'
        ];