I have two vehicles that I change it once a year. One gets about 12,000 miles the other less then 3000. On the low mileage one though I try to drive it at least 10 miles every time I start it. The UOA has been fine on both vehicles, been doing this for several years. A cold winter climate would have a bearing though, cold starts of less then 10 miles would be a consideration for a 6 month interval. Best bet, at 6 months do a UOA to see what it looks like for fuel dilution etc. Worht the price at least once, probably after a winter run.