I have done two of these. One in pink earlier last year, and another recently in blue for the 5th of January.
I like making the little bits on these cakes, the plates, the cups, the bears and the buttons. I think its the little bits that make it again the attention to detail. But can easily spend a whole day making these bits.
I would always advise these things be made in advance so they have time to set. Or even if you have time for some strange reason make them and store them for when you might need them.