Did what? Trained them in business? You'll need to show some support for that. What I can find says that he just kept working them even past the date George Custis gave as the outer limit on their emancipation.
For the record, here's the entire relevant passage from Custis's will:
And upon the legacies to my four granddaughters being paid, and my estates that are required to pay the said legacies, being clear of debts, then I give freedom to my slaves, the said slaves to be emancipated by my executors in such manner as to my executors may seem most expedient and proper, the said emancipation to be accomplished in not exceeding five years from the time of my decease.
As for the delay...it was between the Battle of Sharpsburg and Fredericksburg...so I am willing to give him a little leeway.