If the 3k/3mo is a lot of short trips where the engine never gets fully warmed, OK. Otherwise it is a waste of money, time, and precious oil. But, do 3k/3mo and the oil companies will love you!
As others have said, 12 months or the max mileage allowed by your owner's manual. I do 10,000 mile (not quite a year)oil drain intervals with Schaeffer syn blend or full syn oils & OEM filters and get excellent lab reports.