You can leave Xmas pudding mix overnight, covered. Not so sure about cake mixture as I think some of the air mixed in would be lost, resulting in a flatter, heavier cake. Could you weigh out the fruits and soak them overnight in the booze of choice in one bowl, and weigh out the dry ingredients separately , cover and leave overnight. Then when you are ready to bake, combine them with the butter and eggs as per the recipe you are following? You could prep the tin the day before, too, to save time. Once your GC gave made their wish, the cake could go straight in the oven whilst they continue with their tea.
It would be a shame to go to all the effort and expense of combining everything the night before if it then failed to rise adequately during baking.
Perhaps you could check online using Delia online or Mary Berry. (Just a thought).