As soon as possible. There are many people that shouldn't be having kids.
Within 50 years. We're not quite ready but we are almost there.
51-200 years. Some people are so stupid that they think aborition is wrong.
201-1000 years. This is the most advanced dream of abortionist. It takes lots of time.
"All that stuff I was taught about evolution, embryology, Big Bang theory, all that is lies straight from the pit of hell [the bible] teaches us how to run all our public policy and everything in society." Rep. Paul Broun (R)
As soon as we change women and children into community property. You can't just pull selective abortion out of Plato's ideal State and expect it to work in our society.
Edit: I must assume that there will be some difficulty in telling women that they will be slaves.
The only time that an abortion should ever be "mandatory", i.e. without the woman's express consent, is when she in incapable of both giving and refusing consent (coma or other similar conditions) and the legal next of kin makes the decision.
Rand, Ayn. Philosophy: Who Needs It. New York. New American Library, 1982. Page 8
Amazon.com: Buying Choices: Philosophy: Who Needs It (The Ayn Rand Library Vol. 1)
I'm going to ignore the obvious ridiculousness of the OP and actually try to crazily address it in a serious way...
If we reach such a point in the United States that overcrowding is leading to significant health and living issues that result in a high mortality rate for all ages due to sickness, lack of resources, and lawlessness running rampant then I could see an attempt to make having additional children a reasonable on to make within the given scope of society.
That said, such a situation is about as likely to occur as a unicorn leaping out of my ass leaving a rainbow trail
"I am appalled that somebody who is the nominee...would take that kind of position"
"A court took away a presidency"
"...the brother of a man running for president was the governor of the state..."
It's horrifying because Trump is blunt instead of making overt implications.