Can you give more information? Do you mean with cut out decorations drying or your fondant is hardening too quickly?
If you are wanting mmf decorations to dry, you need to give them a couple days. If it is very humid or hot where you live, that can make the drying take longer. You can put a fan next to them to blow cool air on the decorations to help them dry out a little quicker, but it just takes time!
You could add some gumpaste to your mmf, but I have added gumtex to it on several occassions. Not sure why you read not to. I haven't had any issues with it. I add it to the mmf just like I would regular store bought fondant when I need it to have more elasticity (sp?) and dry quicker.
You can add gum paste - if I'm adding it, I make the mmf like usual and just add gum paste into the amount I need to harden - usually a 50/50 mix. It's still going to take at least 12 hours to harden, that's just the nature of mmf. It depends on so many variables (weather, thickness) sometimes it dries in a half a day, other times it takes 5 days! :)
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