Jade Wang from Google gave a tip in a Google Business Help thread on how to expedite the uploading and listing of photos on your Google Business Maps listing page.
Typically, a business owner would upload photos through managing their page within Google+ or via Google Places. But that process can take a month for the photos to be approved and visible within Google's search results and Google Maps.
Instead, Jade said you can take a "shortcut" by uploading the photos by going to the Photos tab of the Google+ Local listing.
She said the photos should be visible "almost immediately."
So if you want to get photos to show up right away, that is the way to go.
Forum discussion at Google Business Help.
