It's right on the boderline as to whether they will properly mate at three weeks past hatch. You might get one or two that will mate and lay ok, but most will be drone layers. But then you will also get a small percentage of queens that do mate during the first two weeks, that will also turn out to be drone layers. Out of 20 cells I bought in May, I had 3 disappear on mating flights, 17 that mated, of the 17 mated ones, I had one drone layer. She laid a small amount of worker brood, but the vast majority was drone brood.
"I reject your reality, and substitute my own." Adam Savage