My threshold is typically an hour. And this is after all the onboarding and pairing with them for a few features. I throw a month of just interrupt me whenever you need to at any new hire as a lead on a five or so team size on line of business apps. Three days sounds ridiculous for someone to spin and be stuck. That's a huge waste of money and a sign of deep problems imo.

In fact, I'd prefer to discuss sooner than let a new dev on their own for more than a day of work. Discussion brings alignment and saves me time with micro adjustments rather than massive corrections or debates and push back when someone goes off on their own for a long time.