You can use it up to 1 year mark, but that depends on the conditions you drive in. I have mentioned this multiple times on this forum. I suggest you check the owner's manual in this case. Many of them state the conditions in which it could be used up to 6 months and the conditions where you can stretch it up to 1 year.
Many owner's manual usually give following conditions as severe, and you should change the synthetic oil in such conditions at 6 month mark.
- Shorts trips. Definition of short trip changes for winter (15 km or less) and summer (8 km or less).
- Frequent idling for long periods of time, such as stop-and-go driving in heavy traffic
- Prolonged motorway/highway driving in hot weather (usually owner's manual give the number of hours like 2 or more)
- Driving on steep hills or mountains on a regular basis.
- Towing a boat or trailer, carrying heavy objects on a rooftop rack.
- Driving in dusty conditions, such as dirt or gravel roads.
- Prolonged operation at sub-zero temperatures
If you observe these severe conditions, almost all of us fall under it.
Apart from that, I have seen multiple engine builders who show what happens when you blindly stretch the engine oil to 1 year mark without observing the conditions you drive in. You can never find such things through oil analysis report.
The most common problem due to prolong oil change is carbon buildup in the ring land (groves) and in the worst case stuck oil rings in the pistons. This is when even low mileage engines start consuming oil. Then majority of people here start using thick oil which cause things even worse in the long run.
