Benzoyl Peroxide 4% Face Wash [Product Question]

Hi! My dermatologist prescribed me Clindamycin lotion 2x a day and told me to use a Benzoyl Peroxide face wash (4%) with it. Should I be using the Benzoyl Peroxide for both times a day that I wash my face or just one and use a gentle cleanser the other time? Also, how long do you guys let the Benzoyl Peroxide sit? I was just putting it on and washing it off like a regular face wash but I’ve seen some people saying they let it sit for awhile.