I don't control timing. They end up slightly overcooked, for which the crisping on one side compensates. But I do the boiling with the gas turned high so the water boils off asap. Also sometimes I ladle off a bit of the liquid if I feel it isn't going down fast enough. I add oil with the water at the beginning. If the frying pan is being cooperative, then there is a precious window of a few seconds when the bottom of the dumplings are thoroughly crisply fried and they come away from the surface of the pan before burning/sticking again. That is when they are ready.
CLARIFYING THE TECHNIQUE FOR PAN-FRYING DUMPLINGS
1) Use a well seasoned pan. I like to use a black cast iron skillet that is extremely well seasoned, but a non stick pan works perfectly (better).
2) Pre-heat the pan and add a couple of tablespoons of vegetable oil. Put the dumplings in flat side down, and cook for about a minute until the bottoms just start to color lightly.
3) Next add about 1/2 cup of water, raise the heat and cover the pan. Continue cooking, covered the whole time, until most of the water is absorbed and the dumpling filling is almost cooked through. This should take 3-4 minutes if the meat is at room temperature when you start, or a couple of minutes longer if it is frozen.
4) Uncover the pan, let all the water evaporate, add another tablespoon of oil (if necessary) and cook for an additional 2-3 minutes until the dumpling bottoms are well crusted. Serve.
*If the filling is overcooked then you have let them cook covered for too long.
*Conversely if the filling undercooked that they haven't been covered long enough.
*You are really steaming (not boiling) the dumplings, then frying their bottoms crisp.
* If the water doesn't evaporate quickly enough you have used too much.