If I understand clearly you need to capture packets in the specified period. In this case, you can use module Net::PcapUtils, for example:

#!/usr/bin/perl -w

use strict;
use warnings;

use Net::PcapUtils;

my $pk_descr = Net::PcapUtils::open(FILTER => 'ip');
my $period = 1;
my $now = time;
my $till = $now + (60 * $period);
my ($packet, %header);
while (($now = time) < $till) {      
     ($packet, %header) = Net::PcapUtils::next($pk_descr);
     print "Got packet: $packet !!!";
}
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Hope it helped.