Group posts under one div if published on the same date

I’m trying to figure out how to create sort of a timeline effect, by wrapping posts that were published on the same day with a div.

Ex.

[Code moderated as per the Forum Rules. Please use the pastebin]

The closest I’ve come to finding a solution for this is this thread on StackOverflow, but I wasn’t able to make that work.

A huge thanks in advance to anyone that might be able to help me figure this out.