How long will it take till I make money from niche sites?

I started out building a niche site, inspired by Grizzly and thr UniversityKid, and I want to make more of them in the next weeks. 7 months from
now I have to start getting money and Im prepared to work for it in a restaurant, but is there a chance of making a low monthly sufficient salary with niche sites in 6/7 months?How many sites should I build and how many backlinks per day to reach this goal?