I am by no means authoritative or a records keeper, but I can help a little bit. I have climbed in and around Leavenworth, the Stuarts, etc., since the early 1970s. By that time I personally knew of two parties that had done the route car to car (Snow Lakes Parking Lot) in one long day. I climbed the route once in the same fashion (car to car-SLPL) in the early 1990s. My partner and I did it in about 15 hours if memory serves me right. We were not really going for speed, but we did keep up a steady gait on the trail. We had day packs. If we had focused on speed I know we would have knocked off several hours. But we had a good time. So one can take from my posting that the challenge has been around for several decades and is within the realm of a team of ordinary climbers. Hope this helps.
Hey thanks for you response Bob. Ya me and partner just had a similar experience. We just did a car to car of the Stanley burgner and completed it in 14:55. We weren't activity trying to go for speed but rather just wanted to focus on staying moving and efficient. I definitely think that it can be done faster. Thanks for letting me know about how many people try to do it in such fashion.