Hours?
Get rid of the checklist mentality right now. It won’t serve you well when pursuing a medical school admission.
Shadow enough that you have good feel for the various different aspects of the profession and the differences among various specialties, You must be able to explain to someone [who is a physician, a med student] what you’ve learned from those experiences and how it impacts your decision to pursue medicine.
Most applicants have somewhere between 50 and 100 hours of shadowing.