BlogPost.php

<?php

final class BlogPost
{
    private $created;
    private $publish;

    public function __construct()
    {
        $this->created = new DateTime('now');
    }

    public function markForPublishing(DateTime $publish)
    {
        $this->publish = $publish;
    }

    public function isPublishedOn(DateTime $reference)
    {
        return $this->publish instanceof DateTime && $this->publish >= reference;
    }

    public function getCreated()
    {
        return $this->created;
    }
}

WorkingWithDates.feature

Feature: Blogpost date example
  In order to see if an article is published
  As an author
  I need to be able to check if a blog post has been published

  Scenario: Not yet published blogpost
    Given a blogpost
     When I mark it for publishing "tomorrow"
      And I check if the blogpost is published "now"
     Then it tells me the blogpost is not yet published

  Scenario: Published blogpost
    Given a blogpost
     When I mark it for publishing "now"
      And I check if the blogpost is published "tomorrow"
     Then it tells me the blogpost is published