https://www.musical-u.com/learn/how-long-does-it-take-to-learn-musical-intervals/
Depending on your starting point with interval ear training, you will be able to start applying your new interval recognition skills after just a week or two of practice. However, as you see the benefits of interval ear training, you will want to continue – not declare yourself finished with it! https://www.musical-u.com/learn/how-long-does-it-take-to-learn-musical-intervals/