This's an excellent question!
Mazda has Flexible oil change interval been set as the default for 2017 CX-5. First thing I'd check on a potential target of a brand-new 2017 CX-5 is to check Maintenance Monitor and see if oil change schedule has been set to "Flexible". If it does, check the mileage left on oil life. In theory for 2017/2018 CX-5 the oil change warning should come up at the maximum of 7,500 miles or 12 months whichever comes first. If a 2017 CX-5 has been sitting there for 1 year, the oil change warning should be displayed very soon.
But 2017 CX-5 has been only available since April 2017. Chances are very slim to get one sitting for more than 12 months.
Yeah oil is supposed to get changed depending on both mileage AND time. Make sure to use Mazda Moly oil if you plan to change factory oil early for a peace of mind.