What is the regulation that covers when RC Officers must take/pass their first APFT?

CPT (Join to see), it is the same FM and TCs for the rest of the Army (FM 22-20 and TC 3-22.20). However, the regulation you're probably looking for is the one that covers the retention/reenlistment program (AR 601-280) which spells out BARs and separation actions regarding failure to maintain HT/WT and APFT standards.

If the soldier has been assigned to a unit, then the enforcement of that action is on the shoulders of the unit leadership. If they are part of the IRR (assigned to a USAR holding company prior to basic course attendance), then they are subject to enforcement, but rarely does that ever happen ... they'll be brought back under the control of a commander when they arrive at the basic course.

If the soldier is arriving at the unit without being in compliance with physical fitness standards, then your commander needs to have a conversation with the recruiters regarding this.

Bottom line - if they need help, give it to them. They are just starting out and probably need to be given the benefit of the doubt. If that has already happened and you're at the point of washing your hands, then the above mentioned regulation should help to give a firmer wake-up call (putting a BAR in on the soldier) or how to properly start separation actions.

TRADOC 351-10 outlines APTF requirements for graduation from Army courses. I would highly suspect that they be required to pass before attending. Semper Fi