Flipper: Should I Get This Before or After Dental Implant Surgery?

I am having a tooth extraction, bone graft, and finally a dental implant. My problem is with the flipper. I have not had the surgery yet. But my oral surgeon wanted me to get the flipper done and bring it in at the time of surgery so that he can adjust it. However, my dentist wants his assistant to do the flipper AFTER surgery. I feel like I should get the impression done before hand with the dentist and have the flipper done by a lab so that my oral surgeon can see it and adjust it.Are my concerns legitimate? I have to wear this for 6 hours a day per my oral surgeon for 3-4 months. Then have the implant posts done and the wait another 3-4 months before the final implant crown. But the dental assistant at my general dentist thinks I only need to wear it for 2 hours a day. Who is right? And which way should I have the flipper made?Thanks for any advice.