While there are ways to exit a blog successfully (i.e. selling your blog), you should only start a second blog if you have enough time to dedicate to building the blog.
How much time is required to scale a blog?
This will vary based on your niche, relevant expertise, and the degree to which you choose to outsource content.
If you are still working a full-time job, I would generally advise against starting a second blog, even if you are outsourcing much of the writing.
For many bloggers, being able to quit their first job is one of the greatest benefits of building a successful blog. It is less of a clear financial gain and more of a lifestyle shift that certain people (myself included) appreciate.
However, it is possible to run multiple blogs while working a full time job (or not spending much time focused on the blogs yourself) if you have the money and experience to hire a great team.
This strategy is more of an investment in blogging, and less of a lifestyle hack.
If you are interested in systematizing the blogging process and building a larger business around a series of blogs, you might look into building a niche website portfolio.
Regardless of who is actually doing the work, blogs do require significant effort to become successful. And while there are some synergies between sites (you can use the same writers to write content for both sites, you can duplicate website formatting to get a fast start, you can use previously validated niche keyword research from your first blog to boost your second one, etc.), for most bloggers, it is wise to stick to one blog unless you have an abundance of time to spend on a second blog.