If you want to set the date of an entry to something other than the present, you can use the schedule feature in WordPress.
Look for the Publish box on the Add New screen. Click the Edit link to reveal date and time fields.
Modify the date and time to and click OK backdate your entry, or schedule it for a later date. Click Publish.
If you scheduled the entry for a later date, you’ll see the date that you’ve set after you click OK. The Publish button changes to a Schedule button. Click Schedule to save the entry.
If a post has been scheduled for a future date, it will not appear on your site until the scheduled date and time. This is a great feature to have content automatically published to your site while you are away.