does it matter what kind of fondant you use when you want to use the steamer for a shiny finish. Can i use MMF and how long should i steam it for?..

You are just apssing the steamer over it briefly, back and forth a couple of times. I don't know about MMF. I quit using it a long time ago. Actually, I haven't had the need to steam in awhile. I think I did it on Satin Ice only. It's a do it until it is shiny enough thing. but be careful, or you will melt it.