what is the legal guideline for creditors reporting delinquencies to
CRA's. when can creditors report a delenquencies? can they report when
payment is not received by exactly the due date? 10 days after due
date? 60 days? what if partial paymets is already made. Can they
report delinquecy when 100% is not paid? 50%? is there a legal
guideline by Federal government or state of California?

I doubt that there's much of a guideline.  I once had to explain to a
mortgage company why I didn't pay a $3.92 Sears bill on-time (try:
stamp = more than finance costs).