Christmas cakes - do you leave your marzipan to dry before icing with fondant icing?

[Cadbury]

I know you are suposed to do this with Royal icing on the top, but do I need to leave it to dry with the ready to roll fondant stuff, and if I don't,what would happen to the cake? Will it get discoloured?

Anyone help? I have an hour to get this done while dd2 sleeps.

I ususally leave a day or two inbetween, just to ensure the cake doesn't discolour. I think it has something to do with the almond oil in the marzipan but may be wrong.

thanks

I ususally leave a day or 2, but this year wil have to do it a bit quicker...need cakes decorated to take ot school before the weekend!