The duty to retreat has no application but other aspects do.
“Under Florida’s stand your ground law, a person is immune from criminal prosecution when using justifiable force to protect oneself from another persons use of imminent unlawful force against them.”
http://www.southfloridacriminallawyer-blog.com/2012/03/floridas-stand-your-ground-law-explained.html
The term “stand your ground” is being used to refer to the entire Florida law dealing with self-defense, after having been amended to deal with the duty to retreat.
But in this case, based on what Zimmerman is claiming as his defense, the relevant law is the same in all states. The particular “stand your ground” concept has no application to this case, based on what Zimmerman is saying happened.