At an Ohio bank I once worked for, we got an opinion from our counsel about late fees for consumer loans. The Ohio Retail Installment Sales Act (at the time) set a 10-day grace period for so-called three-party indirect loans, while Ohio's version of the UCC required a "reasonable" time (or similar language). As our attorney told us, since ORISA sets 10 days as its standard, that seems "reasonable" & probably a good yardstick to use for other consumer loans.
This was 20+ years ago, so the law may have changed -- check with your legal counsel or look up the current law thru
www.ohio.gov.