When to leave my 9 to 5

I am currently working 32 hours per week at a 9 to 5 job that I don’t like much but offers good benefits for my family. I am a psychologist and coach and have been building my practice for the last several years on the side. I currently see about 8 clients per week. I’ve been at this number of clients for about 6 months now without additional growth. I’ve been working on creating other income streams outside the 1:1 therapy/coaching setting and have self-published a book that will be released next month. A previous business coach advised not to quit my 9 to 5 until my business was making at least 75% of the income from my 9 to 5 job. My business made about 20% of my 9 to 5 job this year (my best year yet). Do you have advice on how to know when to quit my day job and transition to my passion (my business) full-time? Thank you!