And not only was this giant cake built by hand, it was cooked by hand as well. In survival mode.
That means they had to gather a lot of ingredients. Like, a lot. This is how you cook (or rather, craft) cakes in Minecraft:
That's three buckets of milk, three bunches of wheat, two piles of sugar, and one egg per cake. Now, the giant cake is composed of 28,368 cake blocks, meaning the builder, babybomb, had to harvest 85,908 buckets of milk and bunches of wheat, process 56736 units of sugar cane, and wait around for chickens to lay 28,368 eggs. At least.
And then we haven't even considered the glass panes, red-tinted glass blocks, white wool, and dirt that was required to make the giant cake actually look like a giant cake — all of which also had to be hand-crafted and hand-picked. Considering all that, five months doesn't actually sound that bad.