AI have just covered a 8" cake with milk choc ganache and left it to set overnight, however think its too soft to cover in fondant. Is their anyway to fix this if I need cake by lunchtime tomorrow! I used Cadbury Melts (Australia) for the ganache with 200g choc and 125ml pure cream 'not thickened cream) Any help appreciated as to how I can fix in short amount of time!

AI'm not gonna do math and conversions for your amounts, but when I do ganache, it's by weight for everything. Grams for the chocolate, grams for the cream. Have you made it before? I usually follow the same ratio as making white chocolate ganache, because I like it a little on the stiffer side. So it would be 3 parts, maybe 2.75 parts chocolate to cream.

AI have made white choc ganache and it set really hard. No, this my first milk choc ganache and it would be more like 2:1 so maybe need less cream. I know best to let rest overnight but what is earliest I can use ganache after making? Would it help to go over current ganache with a new batch, but will I have time?

AYep, there's your problem most likely. Milk chocolate very nearly needs to be treated like white when making ganache. I won't use it until it's set up overnight.

I use a 3:1 ratio for white and milk chocolate, 2:1 for dark chocolate.  I don't let the ganache set overnight in the bowl--I apply it to the cake once it starts to thicken to that peanut butter consistency.  Then, I let the ganached cake set over night.  This way, you are only waiting for it to set one time instead of twice.

Sorry, I don't know about applying another coat of ganache over your current ganache...maybe some experts will have an answer for you about that.  Good luck!  

AThanks to you both for your quick replies! Will make another batch now and put on tonight. Fondant in the morning and decorate. Fingers crossed.