Not Accepting Loss of Privileges

My adhd child who is 8 will sometimes choose to earn loss of privileges for a certain amount of hours, however usually he'll choose not to start it until he's ready. He will continue to go play outside, eat snacks, not start chores etc. I'm not sure how to handle him doing that because if I try to stop him, it will turn into a big power struggle, but I remind him that he's choosing the wrong choice and I will not do anything extra for him (like play with him outside or help him open snacks.) Sometimes it takes him hours to get ready to accept those loss of privileges, so what's the point if he chooses to go outside until he's ready? I can't just hold him captive inside.