I want to publish some content in a day, not all of unpublish content at once.
for example I have 20 unpublish content and i want to publish 2 random content in a day at 13:00.
How can I resolve this?
If you aren't concerned with the "random content" portion of your question you could use the scheduler module to accomplish the task - https://drupal.org/project/scheduler which would allow you to set specific times during the day when you wanted content to be published.
(I'm assuming Drupal 7)
2 random pieces of content should publish.