1st time cake decorator, making fruit cakes for christmas. How long before do i cover the cakes in fondant?? Any advice??

Using marzipan as a base (highly recommended, or if you don't like marzipan then use 2 layers of fondant), I have covered fruit cakes up to 5 weeks in advance with no problems, just store in a box to keep out light and keep off dust. In any advent you want to give fondant a couple of days to 'set', so no later than a couple of days ahead of time is my recommendation.