How long does it take to build a mansion in minecraft?

Interior and exterior look great then 3 days of like 3-4 hours depending on how much you thought about your mansion

Well just like real life it all depends on your effort and work speed and if you can hire a team of people standing in front of Home Depot that might also help you tremendously.

It always depends. I usually start off with a small house and keep adding on until it becomes a huge mansion with weeks of work put into it. Or just create a huge skeleton in around 2 hours and fill it in however i want after that.