如何在白天过滤PHP / MySQL中的数据？

I have a PHP script which users submit a post and saves in to the database; I'm storing the date it was posted using time(). I'm trying to figure out a way to filter my data by day. I have a while loop which is returning all the posts that user made which is ordered by date, however what I'm looking to do is have headings of a date for e.g. 10 December 2011 and only have posts that was submitted on that day. I want it only to display the heading if there is data for that day.I have a PHP script which users submit a post a