I seem to have been misunderstood.
As I said, I do not advocate either of the approaches being discussed. Using both hands was suggested to me by one of my TDI instructors in an attempt to get my time lowered as much as possible. I got it to nearly 30 seconds that way. I do not advocate it, and I do not do it that way myself now that I have completed that "speed counts!" certification.
The meet the standards for the agency for which I am currently teaching, students have to do it in 45 seconds, which is pretty fast. I do it so they meet standards, but I focus the instruction on real world situations. I come up behind them and use my long hose primary to blow bubbles by a valve to watch how they react to it. They have to signal the buddy, shut down the appropriate valve (etc.) without losing buoyancy and trim. I do that a lot, because that's where I think the real learning is.
Want to know what makes the biggest difference in how well and how fast you do a valve drill? It's the nature valves on your manifold. Some of them take twice as many turns to open and close as others, and some of them can be very sticky. When I was first learning the valve drill, I used my instructor's backup doubles, with a DiveRite manifold. It was horrible. I had to crank hard to get them to turn--fingertips were worthless--and it took many turns to open and close. My instructor thought I was hopeless. I actually had to rest my left hand part way through turning the left post. Then I bought my own gear with thermo valves and I could nearly spin them through the fewer turns it took. I could do it with ease. Just after that, my instructor had to use his own backup gear, the stuff I had been using before, and he found he couldn't do it, either. He got the valves serviced, and it helped.
