Website development has become a piece of cake today. You can build a custom website very easily, even if you have no prior knowledge of programming. Many companies like Wix provide this type of facility.
But if you look for complex designing. Then there is no time limit. And if you want a professional website, it sometimes takes 2 days to 2 weeks in building even one page.
So, it's totally up to your requirements that how much complex or simple is your website's design and structure.