BAD IDEA
Is it still illegal to print money at home very slowly?
Yes, printing money at home slowly is still illegal. Counterfeiting doesn't get a speed mode for legality.
Printing money at home, whether slowly or at Mach speed, remains illegal because counterfeiting is against the law everywhere. Doing it slowly just means you're taking longer to commit a crime, not avoiding it. If you're caught, the law doesn’t care how patient you were.
Attempting to counterfeit money is a serious crime with severe penalties. Do not try this at home.