My guy charges 2.5 hours, I believe he is the exception though. Alot will depend on the pipes too, Some are a bitch to get off and on, mine go off or on in about ten minutes. Some pipes can take an hour or more to R&R
I checked two HD dealerships--- one was 6-8 hrs and the other was 2.5 hours so I decided to do it myself. Took me 4.5 hours...and it was my first time with home made tools! The 2.5 hours sounds about right. As previuosly stated, exhaust headers ( not your V&H Ovals mufflers) are a time variable but not more than an additional 30 minutes.