Fondant icing on chocolate biscuit cake - how far in advance?

[GrainneWail]

I'm making a cake for next Saturday, 5th. It's two layers, bottom layer chocolate biscuit. I have it made and was thinking of icing it tonight to get it out of the way as the design will be a bit time consuming to finish and I want to leave time next week to do the top sponge layer on Thurs. I'll be doing fondant icing so I'll have to keep the cake at room temperature once it's iced. Would I be better leaving it til Sunday to do it?