I'm a newbie with using gumpaste. I want to make a plaque from gumpaste and attach it to the side of my round layer cake. How do I attach it? And how long should I let the plaque dry before it's hard enough to hang? Thanks for your help!

Let it dry on a curved surface like your cake pan, unless you want it standing flat away from your cake. You can attach it with a bit of gumpaste dissolved in water(gum glue) or attach with royal icing or use melted chocolate or candy melts as glue to attach. overnight or comparable time should be sufficient, especially if you're using Wilton's which seems to dry super fast.

I dont let my plaques dry if they go on a round cake. I just attached them while they are still soft enough and pliable.
I use a bit of gum glue or water to attach. Just don't put too much or it will slide down.
Edna

So now I'm wondering if you can glue a gumpaste plaque to buttercream and fondant both? Or does it just work with fondant?