As the title says I want to know a single word that can be used for a person who expects immediate results?
Off the top of my head I'd say "impatient", although that carries a negative connotation.
You might want to give a little more context in order to find a more suitable word or phrase.
Depending on the context, those might fit:
I guess it can be
eager - at least it will be suitable for the one expecting quick response.