composer require nesbot/carbon

<?php
require 'vendor/autoload.php';
use CarbonCarbon;
$data = new Carbon('2015-08-20', 'America/Sao_Paulo');
$data->setLocale('pt_BR');
echo $data->diffForHumans() .PHP_EOL;

$data->addDays(3);
echo $data->diffForHumans() .PHP_EOL;

há 1 semana
há 6 dias

composer require coduo/php-humanizer

<?php
require 'vendor/autoload.php';
use CoduoPHPHumanizerDateTime;

$data = new DateTime('2015-08-10');
echo DateTime::difference($data, new DateTime()) .PHP_EOL;
echo DateTime::preciseDifference($data, new DateTime()) .PHP_EOL;

3 weeks from now
20 days, 18 minutes, 7 seconds from now