You can change the way the date/time is displayed on your posts by going to the Layout section of your blog’s dashboard.
From there, edit the “Blog Posts” gadget, as shown below:
In the panel that pops up, you can change the dates displayed, as shown below.
Note: If you find that the main post date is shown as a time, rather than an actual date, please try changing the option shown by the second arrow. This is often the case when using a grid based layout on Blogger.