Assuming that you save 1/3rd of your monthly net income, and spend only 2/3rds of it on expenses -- which I believe is already beyond what most people can do --,
and that you are
already frugal (which means that you don't have easily cuttable expenses [*]), you'd need to save twice as long as you planned to live off of those savings. If you wanted a buffer for 4-5 years, you'd need to pinch every penny for 8-10 years, and do that -- presumably -- while you are in your thirties, and raising kids. This can work, but mostly as an exception, I think.
[*] I don't consider expenses that improve health and lifestyle "cuttable" -- organic food, locally produced meat, food supplements / vitamins, therapy, dentist, gym / sports, etc. I've recently learned that even holiday trips (which are insanely expensive, assuming you are not from the US, to the point of being financially injustifiable) are crucial for mental and marital health.