J1 to F1 Question

Hi everyone,

I'm on J1 visa right now and applying for F1. And I've heard that I need to notify USCIS about my status change before I attend my visa appointment in Canada. My question is do I need the approval from USCIS for my visa appointment because it says it takes about 4-6 months for it to be approved. Is it too late to change to F1 now if my J1 expires in August?

Thank you so much for your help!