What you have been doing is a static, or dead release. What you are trying now is more of a dynamic release. Either a static release or a dynamic release can work for you. What you have to be careful of is that you don't lose any back tension during your hold. Most people who use a dynamic release continuously increase back tension during their hold, although the amount of increase may be minuscule if they want a long hold time. In a static release, people lock off their back muscles at full draw, similar to the way you would lock off your back muscles at the top of a pull-up, and, as you say, simply relax the fingers at the time of release.
I don't think you would want to lock off your back muscles and then re-start your draw to conclusion. I think you would either want to steadily increase back tension through conclusion, or lock off your muscles and then release by relaxing your fingers, as you have been doing.
As I said, either the dead release or the dynamic release can be successful for you. I've tried mixing the two, and found that it was the worst of both worlds. Of course, if you can mix them successfully and start winning all kinds of tournaments, then you can re-write the rules to suit yourself