Making money online is not a 'get-rich-quick' scam. Anyone telling you otherwise is probably trying to scam you. If you want to make money by starting a blog, then you will have to work hard and invest a lot of your time into it.
There is no easy way to tell you how soon you would start making money. Some bloggers start making small amounts soon after starting their blogs. Others struggle to get their blogs to take off.
However, those who continuously work and stick to a planned strategy are the ones most likely to see encouraging results very early on.