Change ALL Post Titles to Post Date

I recently imported all of my posts from Tumblr, but because they were all image posts, they had no “official” titles. I would like to make the title of the post the date it was posted. So if it was posted today, the title would be “September 16, 2015.” for example. Is there any way to do this? I have searched everywhere for a plugin and I looked at the database and it may be feasible in there, but the dates aren’t formatted properly and have the time as well. Ideally I would be able to just change the title and not the permalink.

Thanks in advance!