On Tuesday I will go back to the pool and do this exercise again until I get it right. I cannot hold my breath for 50 seconds while swimming or even walking. I am practicing and working on that. My surface dive skills need some work as well.
ladyfish,
In post #15 above I described a similar skill we were required to do, and encouraged you to keep attempting to pass yours, as success will surely come, eventually. I neglected to mention that, as my open water course was a university PE course, physical conditioning was a huge part of it. We were swimming (with and without snorkeling gear) and running and doing other exercises from the start. For example, we were practicing a timed skill, called the "Skin Diving Circuit," which involved repeated surface entries, surface dives (to the bottom of the deep end), removal of weight belt (at the bottom of the deep end), and retrieval and replacing of weight belt, all the while swimming repeated laps and climbing out of the pool. So, from the start of the course we were increasing our endurance and stamina. So, as we attempted to pass skills such as the "Thimble Test," it became increasingly easier to do, due to our constant and improving physical conditioning.
This kind of training you're undergoing is made so much easier if you are pursuing a regimen of physical conditioning.
Safe Diving,
rx7diver
P.S. Lest you think this kind of training is only for the "kids" among us, I was a 31-year-old grad student when I took my course.