I think F&F and Springfield will both officially "open" the same day, so that the swarm of guests coming for F&F will at least have some new places to eat.
Another thing that Universal has to watch out for....Disney will be celebrating Disneyland's 60th in May, with a huge celebration, big marketing campaign, overlays, decorations, refreshed rides, shows, parades, etc. So I think Universal will have to open both before that.