The update, added on Friday and announced by +Jon Moon of Google, makes finding groups of photos by date with a click of a button.
You'll find the menu in the Highlights page on Google+ Photos, at the top-right corner. The date shown will be the current month, and clicking will bring up a scrollable date picker which is sorted reverse chronologically and goes all the way back to the 70s! Now who said time travel isn't possible?
It's a lovely little new addition that not everyone might have noticed since the roll out on Friday. I've already found it to be quite useful, and now I'm wondering how I lived without it before!
Let us know what you think of the new drop-down calendar for Highlights in the comments!
Source: Jon Moon's announcement post