On Monday, a city judge rescinded his order calling for the 60-year-old singer to return to Tucson to serve 48 consecutive hours in the Pima County Jail.
Ross, who pleaded no contest in February to a drunken-driving charge, arranged to serve her jail sentence in Greenwich, where she lives.
But based on an account from Greenwich police, Tucson City Court Magistrate T. Jay Cranshaw found that she failed to serve 24 consecutive hours as required by Arizona law.
Ross spent 22½ hours at the Greenwich jail between Feb. 9 and Feb. 10 before being released because there was no female guard on duty for the remaining 1½ hours.
Defense lawyers and prosecutors told Cranshaw during a hearing last week that Ross should be credited with having served her full sentence.
In all, she served 47 hours in the custody of Greenwich police over a three-day span, Cranshaw found.
In the ruling Monday, Cranshaw said Ross was not at fault for her early release.
"It's the right thing to do," said James Nesci, one of Ross' attorneys. "We still don't know why there was a discrepancy. It doesn't matter. She has completed the sentence. She's done."
The former lead singer for the Supremes was arrested Dec. 30, 2002, after a driver called to report a car traveling south in the northbound lanes outside Tucson.
Tests showed Ross had a blood-alcohol level of 0.20 percent, police said. Arizona's legal limit for drivers is 0.08.