Sign in to FamilySearch.org and then hover over Memories at the top of the screen and click Gallery. By default it comes up in a grid view. Click the three lines icon in the top right to change to a thumbnail view.
Now you can click Add Event Date or Add Event Place to add more details about a photo, audio recording, document, or story. Just one more little detail that can help add value to the items you add to Memories.
I sorta expected that I'd also see the option to add the date and place if I had a particular item open in the viewer, but it doesn't seem to be any other place besides the thumbnail view in the Gallery.
Now, if I only knew when and where most of the photos I have of my ancestors were taken!