There's no set time really. If you're a fast writer and have a simple story idea, it could be as little as a couple of months. But if you have a full - time job and can only write on weekends, and your novel has a lot of intricate plotlines, it could take several years. It also depends on how often you get writer's block.
The time it takes to write your first novel depends on many factors. Your writing speed, the complexity of the story, and the amount of time you can dedicate to it all play a role. Generally, it could take anywhere from six months to two years.