Assuming you are being seated at Citrico's by 5:15, and do not have slow eaters, and catch a bus to DHS fairly quickly after arriving outside at the GF bus depot... you should be at the gates of DHS shortly before 7.
Whether or not this is early enough to get in for a prime seat at Fantasmic, probably depends on the crowd that day.
We never wait in line for seating for Fantasmic, as I have seen it no less than about twenty-twelve times and am fine with whatever seats we get. So I am not the best gauge of how long before the show you should get in line for prime seats....