Fully synthetic here from when I first bought mine. I have ran it up until about 7k miles and done an oil analysis and could've safely ran a few more hundred miles until it would really need an oil change.

 

What about time interval? I've had Royal Purple synthetic sitting in my engine for about 5.5 months now but have only driven the car ~2k miles. Should I bother to change it after 6 months?

 

You can get it analyzed and see how it's fairing. So the next time, you'll know how your oil will be at 5.5 months ~2k miles.

 

On the other side of the fence here, to be fair i've done UOA's for years now and have managed to go as high as 15k with no issue. Although i only did that once, mainly for my own peace of mind, even if the analysis showed things were fine.

 

Your local dealership has a bunch of thieves or idiots who shouldn't be in the car service business. Take a pick.

 

+1. Oil analysis is the way to go.

 

Synthetic is not thinner than conventional. A 5w-30 is a 5w-30. The viscosity of the oil (at cold and operating temperature) will fit into the same range, synthetic or dino.

 

As Jeff92se said, get it analyzed to see how the oil is doing. However if you're still under warranty, change it after 6 months to keep the warranty. Once you're out of warranty you can do whatever you feel like doing!