Hi Jonas,
in my experience, preparing for a consulting interview so that you can land at least an offer will require 150-200 hours starting from zero on your own. This should cover:
- Define a calendar on how to prepare
- Learn the basic frameworks/theory for cases
- Learn how to answer to the fit part (including your questions at the end for the interview)
- Learn how to answer to market sizing questions
- Practice math and graph analysis
- Read examples of cases
- Practice the cases, fit and communication skills live
The time you should spend thus would depend on how much time you have available to dedicate to consulting. Typical situations include:
- You are full time on preparation and can dedicate 4 hours every single day (even if you have more time you are likely not productive anyway if you spend more than 4 hours on consulting prep per day) --> 6 weeks
- You are working and can dedicate 2 hours per day during weekdays and 4 hours per day during weekends --> 10 weeks
- You are working and can dedicate 1 hours per day during weekdays and 2 hours per day during weekends --> 20 weeks
In case you can count on a very experience partner/former consultant/expert for your preparation, you can assume that every hour you will do with him/her will be worth between 2-15 hours on your own, thus decreasing significantly the preparation time.
Hope this helps,
Francesco