No, please do NOT quit your job to prepare for a case interview where you have a 1% chance of getting in!
Expect to spend over 100 hours total to prepare properly for these interviews (assuming you even get an interview), spread out over at least a couple of months. We all do this while working or studying full times (and usually while applying to other companies as well). This means no personal life for a while, but it is worth it. What nobody does however, is quit everything to focus 100% on case interview prep. It may work, but odds are it won't. Please don't do that.