The fastest boarding I ever experienced was a NW A320 on DEN-DTW about 2007/2008. They boarded a full flight in 12 minutes.

The inbound was late and once the plane arrived and deboarding, the GA made an announcement basically saying:
"OK, listen-up this is important. We are going to have to do an extremely expedited boarding process. This flight has to be off the gate in 18 minutes otherwise the crew will reach the end of their duty limit and we will not be able to get out of here tonight. You all really want to get to DTW tonight, the crew really wants to get back to DTW tonight, so we are going to make this happen. So listen-up.
We are going not pre-board anyone for first class or anything. We are boarding this back to front in 5 row increments at a time. Only go when we call you, put your bags in your zone and seat down immediately.
If we all work together we can do this"

And guess what it happened. They had the FAs positioned to help get back stowed, barking orders at passengers, and closing bins as they filled-up back to front. FAs were barking orders on the PA.
It worked.

12 minutes, they got the last pax on board, closed the door immediately and pulled the jetway.

In the hundreds of flights, I've never seen anything like that but it worked.

This is a lot better than the stupid 40 minutes it took to board an MD-88 in ICT last week since no one was policing the OH bin space and way too many people brought bags on board well after the bins were full and ended up having to swim upstream and gate check.