My best guess would be about 10 minutes.
I have only had to speed reload once in my life while hunting. I was hunting about 20 feet in the air in a tree stand that myself and a few friends built from lumber. It was a very comfortable stand.
I had a big doe come in and I missed her. Don't know how I missed(ya right), but I missed. The doe acted like nothing happened. So I decided a speed relaod was necessary. I put the powder down the barrel and started the PRB with a short starter. When I pulled the ramrod from the rifle I gave it a little flip so that it would clear the rifle. The problem was not only did it clear the rifle, but it cleared the entire tree stand. I threw it out of the stand and onto the ground.
So I climbed down the stand. The doe was at about 60 yards and she did not spook. Believe it or not. So I climbed back uo the stand with the ramrod in my teeth. Pushed the ball down the bore and shot the doe. And all that took about 10 minutes.
So my speed reloading is about 10 minutes. Tom.