I've read a number of times that you can ask for and get the burger for dinner. And it was a very yummy burger when I had it last August.
Our lunch was at 3:00; I don't know what time they do the switch, but I'd guess around 4:00. It worked well for us to have a late lunch on our DHS day. We enjoyed that meal, then had plenty of time to do some attractions and wait for Fantasmic at 8:00. It was easier than trying to rush there after eating dinner at a regular time of 6:30 or so.