Just after Hagrid's opened, we were there at Christmas and got in line at night. We were at a dead stop just inside the castle in the room with the dragon mural. Eventually, the ladies in front of us decided to leave the line.
We waited in the line for easily 75 - 90 minutes and when we got to the single rider merge, we got there at the same time as the ladies that had left the standby line. We were a party of 5, so one rode with one from our group. We all though, "Ha! They didn't save any time at all!" until they told us it was their 2nd ride in the time it took us for 1 lol
But overall, I agree with @CAPSLOCK, the 2-seater rides can put the single rider lines at a disadvantage. I do wonder if Hagrid's changes that formula slightly since you may have a party of two wait together in standby, but when boarding say they are parties of 1 so they each get the bike.
Dreams Unlimited Travel is committed to providing you with the very best vacation planning experience possible. Our Vacation Planners are experts and will share their honest advice to help you have a magical vacation.