The Help on placing photos states,
If your GPS file and your photos all have correct timestamps, then you must adjust the offset either manually, or by placing one of the photos in the correct location, clicking on the pin, and selecting “update other photos”. This should update all locations, and save the offset for future use.
When I use the photo placement feature, there is no "update other photos" button anywhere that I could see. I'm definite about one of the photos and can place it correctly -- don't want to place all photos by hand -- that's tedious. Timestamps should be correct.