Wait for the marzipan to dry on the cake for at least 24 hours. Brush the marzipan with a bit of water, then spread the royal icing. Allow the icing to harden, then decorate as desired.
Great recipe, thanks for posting. I left it to stiffen slightly before applying...my first time not using the ready rolled icing. Looks and smells so much better... - 02 Sep 2015