I shadowed for 10 hours only and got interviews from all 5 schools I applied to. I did apply this cycle so perhaps schools were lenient due to the pandemic. I suggest using as many avenues possible to learn about the profession, and to mention them in your application (podcasts, books, informational interviews, online shadowing, etc). Shadowing is mandatory because it demonstrates understanding of what it means to be an optometrist and most importantly, whether you can envision yourself as one.