My 2011 Buick Regal's manual says simply:
"When the CHANGE ENGINE OIL SOON message displays, service is required for the vehicle as soon as possible, within the next 1,000 km/600 miles. If driving under the best conditions, the engine oil life system might not indicate the need for vehicle service for more than a year. The engine oil and filter must be changed at least once a year and the oil life system must be reset." (Emphasis mine.) No mention of severe service vs. regular service.
My OLM indicates I could go 6000 miles on a fill. My dealer says they're recommending 5000 miles at the outside.